diff --git a/services/history-v1/api/controllers/project_import.js b/services/history-v1/api/controllers/project_import.js
index 5dec84d843..9d47fe06a9 100644
--- a/services/history-v1/api/controllers/project_import.js
+++ b/services/history-v1/api/controllers/project_import.js
@@ -130,7 +130,9 @@ async function importChanges(req, res, next) {
   }
 
   if (returnSnapshot === 'none') {
-    res.status(HTTPStatus.CREATED).json({})
+    res.status(HTTPStatus.CREATED).json({
+      resyncNeeded: result.resyncNeeded,
+    })
   } else {
     const rawSnapshot = await buildResultSnapshot(result && result.currentChunk)
     res.status(HTTPStatus.CREATED).json(rawSnapshot)
diff --git a/services/history-v1/storage/lib/persist_changes.js b/services/history-v1/storage/lib/persist_changes.js
index b17d7d8b37..47798531b2 100644
--- a/services/history-v1/storage/lib/persist_changes.js
+++ b/services/history-v1/storage/lib/persist_changes.js
@@ -82,6 +82,7 @@ async function persistChanges(projectId, allChanges, limits, clientEndVersion) {
 
   let originalEndVersion
   let changesToPersist
+  let resyncNeeded = false
 
   limits = limits || {}
   _.defaults(limits, {
@@ -166,12 +167,11 @@ async function persistChanges(projectId, allChanges, limits, clientEndVersion) {
         const actualHash = content != null ? getContentHash(content) : null
         logger.debug({ expectedHash, actualHash }, 'validating content hash')
         if (actualHash !== expectedHash) {
-          throw new InvalidChangeError('content hash mismatch', {
-            projectId,
-            path,
-            expectedHash,
-            actualHash,
-          })
+          logger.warn(
+            { projectId, path, expectedHash, actualHash },
+            'content hash mismatch'
+          )
+          resyncNeeded = true
         }
 
         // Remove the content hash from the change before storing it in the chunk.
@@ -300,6 +300,7 @@ async function persistChanges(projectId, allChanges, limits, clientEndVersion) {
       numberOfChangesPersisted: numberOfChangesToPersist,
       originalEndVersion,
       currentChunk,
+      resyncNeeded,
     }
   } else {
     return null
diff --git a/services/history-v1/test/acceptance/js/api/project_import.test.js b/services/history-v1/test/acceptance/js/api/project_import.test.js
index 216fb527fa..fb173238f8 100644
--- a/services/history-v1/test/acceptance/js/api/project_import.test.js
+++ b/services/history-v1/test/acceptance/js/api/project_import.test.js
@@ -52,6 +52,6 @@ describe('project import', function () {
       })
 
     expect(importResponse.status).to.equal(HTTPStatus.CREATED)
-    expect(importResponse.obj).to.deep.equal({})
+    expect(importResponse.obj).to.deep.equal({ resyncNeeded: false })
   })
 })
diff --git a/services/history-v1/test/acceptance/js/storage/persist_changes.test.js b/services/history-v1/test/acceptance/js/storage/persist_changes.test.js
index aa56dc8c2a..0bb8836cc1 100644
--- a/services/history-v1/test/acceptance/js/storage/persist_changes.test.js
+++ b/services/history-v1/test/acceptance/js/storage/persist_changes.test.js
@@ -58,6 +58,7 @@ describe('persistChanges', function () {
       numberOfChangesPersisted: 1,
       originalEndVersion: 0,
       currentChunk,
+      resyncNeeded: false,
     })
 
     const chunk = await chunkStore.loadLatest(projectId)
@@ -106,6 +107,7 @@ describe('persistChanges', function () {
       numberOfChangesPersisted: 2,
       originalEndVersion: 0,
       currentChunk,
+      resyncNeeded: false,
     })
 
     const chunk = await chunkStore.loadLatest(projectId)
@@ -147,6 +149,7 @@ describe('persistChanges', function () {
       numberOfChangesPersisted: 2,
       originalEndVersion: 0,
       currentChunk,
+      resyncNeeded: false,
     })
 
     const chunk = await chunkStore.loadLatest(projectId)
@@ -213,7 +216,7 @@ describe('persistChanges', function () {
       expect(result.numberOfChangesPersisted).to.equal(1)
     })
 
-    it('rejects a change with an invalid hash', async function () {
+    it('turns on the resyncNeeded flag if content hash validation fails', async function () {
       const limitsToPersistImmediately = {
         minChangeTimestamp: farFuture,
         maxChangeTimestamp: farFuture,
@@ -235,9 +238,13 @@ describe('persistChanges', function () {
       )
       const changes = [change]
 
-      await expect(
-        persistChanges(projectId, changes, limitsToPersistImmediately, 0)
-      ).to.be.rejectedWith(storage.InvalidChangeError)
+      const result = await persistChanges(
+        projectId,
+        changes,
+        limitsToPersistImmediately,
+        0
+      )
+      expect(result.resyncNeeded).to.be.true
     })
   })
 })
diff --git a/services/project-history/app/js/HistoryStoreManager.js b/services/project-history/app/js/HistoryStoreManager.js
index fe9c9e3d2d..bb41dfb3c0 100644
--- a/services/project-history/app/js/HistoryStoreManager.js
+++ b/services/project-history/app/js/HistoryStoreManager.js
@@ -249,7 +249,7 @@ export function sendChanges(
       method: 'POST',
       json: changes,
     },
-    error => {
+    (error, response) => {
       if (error) {
         OError.tag(error, 'failed to send changes to v1', {
           projectId,
@@ -261,7 +261,7 @@ export function sendChanges(
         })
         return callback(error)
       }
-      callback()
+      callback(null, { resyncNeeded: response?.resyncNeeded ?? false })
     }
   )
 }
diff --git a/services/project-history/app/js/UpdatesProcessor.js b/services/project-history/app/js/UpdatesProcessor.js
index b52fac7af6..a76241d7ca 100644
--- a/services/project-history/app/js/UpdatesProcessor.js
+++ b/services/project-history/app/js/UpdatesProcessor.js
@@ -85,7 +85,7 @@ export function startResyncAndProcessUpdatesUnderLock(
         })
       })
     },
-    (flushError, queueSize) => {
+    (flushError, { queueSize } = {}) => {
       if (flushError) {
         OError.tag(flushError)
         ErrorRecorder.record(projectId, queueSize, flushError, recordError => {
@@ -132,7 +132,7 @@ export function processUpdatesForProject(projectId, callback) {
         releaseLock
       )
     },
-    (flushError, queueSize) => {
+    (flushError, { queueSize, resyncNeeded } = {}) => {
       if (flushError) {
         OError.tag(flushError)
         ErrorRecorder.record(
@@ -167,7 +167,15 @@ export function processUpdatesForProject(projectId, callback) {
               'failed to clear error'
             )
           }
-          callback()
+          if (resyncNeeded) {
+            logger.warn(
+              { projectId },
+              'Resyncing project as requested by full project history'
+            )
+            resyncProject(projectId, callback)
+          } else {
+            callback()
+          }
         })
       }
       if (queueSize > 0) {
@@ -198,7 +206,7 @@ export function resyncProject(projectId, callback) {
           releaseLock
         )
       },
-      (flushError, queueSize) => {
+      (flushError, { queueSize } = {}) => {
         if (flushError) {
           ErrorRecorder.record(
             projectId,
@@ -247,7 +255,7 @@ export function processUpdatesForProjectUsingBisect(
         releaseLock
       )
     },
-    (flushError, queueSize) => {
+    (flushError, { queueSize } = {}) => {
       if (amountToProcess === 0 || queueSize === 0) {
         // no further processing possible
         if (flushError != null) {
@@ -298,7 +306,7 @@ export function processSingleUpdateForProject(projectId, callback) {
     ) => {
       _countAndProcessUpdates(projectId, extendLock, 1, releaseLock)
     },
-    (flushError, queueSize) => {
+    (flushError, { queueSize } = {}) => {
       // no need to clear the flush marker when single stepping
       // it will be cleared up on the next background flush if
       // the queue is empty
@@ -339,18 +347,34 @@ _mocks._countAndProcessUpdates = (
     }
     if (queueSize > 0) {
       logger.debug({ projectId, queueSize }, 'processing uncompressed updates')
+
+      let resyncNeeded = false
       RedisManager.getUpdatesInBatches(
         projectId,
         batchSize,
         (updates, cb) => {
-          _processUpdatesBatch(projectId, updates, extendLock, cb)
+          _processUpdatesBatch(
+            projectId,
+            updates,
+            extendLock,
+            (err, flushResponse) => {
+              if (err) {
+                return cb(err)
+              }
+
+              if (flushResponse.resyncNeeded) {
+                resyncNeeded = true
+              }
+              cb()
+            }
+          )
         },
         error => {
           // Unconventional callback signature. The caller needs the queue size
           // even when an error is thrown in order to record the queue size in
           // the projectHistoryFailures collection. We'll have to find another
           // way to achieve this when we promisify.
-          callback(error, queueSize)
+          callback(error, { queueSize, resyncNeeded })
         }
       )
     } else {
@@ -376,15 +400,21 @@ function _processUpdatesBatch(projectId, updates, extendLock, callback) {
         { projectId },
         'discarding updates as project does not use history'
       )
-      return callback()
+      return callback(null, {})
     }
 
-    _processUpdates(projectId, historyId, updates, extendLock, error => {
-      if (error != null) {
-        return callback(OError.tag(error))
+    _processUpdates(
+      projectId,
+      historyId,
+      updates,
+      extendLock,
+      (error, flushResponse) => {
+        if (error != null) {
+          return callback(OError.tag(error))
+        }
+        callback(null, flushResponse)
       }
-      callback()
-    })
+    )
   })
 }
 
@@ -536,6 +566,8 @@ export function _processUpdates(
           if (error != null) {
             return callback(error)
           }
+
+          let resyncNeeded = false
           async.waterfall(
             [
               cb => {
@@ -646,7 +678,13 @@ export function _processUpdates(
                     projectHistoryId,
                     changes,
                     baseVersion,
-                    cb
+                    (err, response) => {
+                      if (err) {
+                        return cb(err)
+                      }
+                      resyncNeeded = response.resyncNeeded
+                      cb()
+                    }
                   )
                 })
               },
@@ -657,7 +695,11 @@ export function _processUpdates(
             ],
             error => {
               profile.end()
-              callback(error)
+              if (error) {
+                callback(error)
+              } else {
+                callback(null, { resyncNeeded })
+              }
             }
           )
         }
diff --git a/services/project-history/test/unit/js/UpdatesManager/UpdatesProcessorTests.js b/services/project-history/test/unit/js/UpdatesManager/UpdatesProcessorTests.js
index 137169bfcf..6f148e5a8d 100644
--- a/services/project-history/test/unit/js/UpdatesManager/UpdatesProcessorTests.js
+++ b/services/project-history/test/unit/js/UpdatesManager/UpdatesProcessorTests.js
@@ -13,7 +13,7 @@ describe('UpdatesProcessor', function () {
     }
     this.HistoryStoreManager = {
       getMostRecentVersion: sinon.stub(),
-      sendChanges: sinon.stub().yields(),
+      sendChanges: sinon.stub().yields(null, {}),
     }
     this.LockManager = {
       runWithLock: sinon.spy((key, runner, callback) =>
@@ -109,7 +109,7 @@ describe('UpdatesProcessor', function () {
       this.queueSize = 445
       this.UpdatesProcessor._mocks._countAndProcessUpdates = sinon
         .stub()
-        .callsArgWith(3, this.error, this.queueSize)
+        .callsArgWith(3, this.error, { queueSize: this.queueSize })
     })
 
     describe('when there is no existing error', function () {