diff --git a/changelog.d/7815.bugfix b/changelog.d/7815.bugfix
new file mode 100644
index 000000000..3e7c7d412
--- /dev/null
+++ b/changelog.d/7815.bugfix
@@ -0,0 +1 @@
+Fix detection of out of sync remote device lists when receiving events from remote users.
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 930ae088c..e43bccd72 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -61,6 +61,7 @@ from synapse.logging.context import (
     run_in_background,
 )
 from synapse.logging.utils import log_function
+from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.replication.http.devices import ReplicationUserDevicesResyncRestServlet
 from synapse.replication.http.federation import (
     ReplicationCleanRoomRestServlet,
@@ -789,15 +790,25 @@ class FederationHandler(BaseHandler):
                     resync = True
 
             if resync:
-                await self.store.mark_remote_user_device_cache_as_stale(event.sender)
+                run_as_background_process(
+                    "resync_device_due_to_pdu", self._resync_device, event.sender
+                )
 
-                # Immediately attempt a resync in the background
-                if self.config.worker_app:
-                    return run_in_background(self._user_device_resync, event.sender)
-                else:
-                    return run_in_background(
-                        self._device_list_updater.user_device_resync, event.sender
-                    )
+    async def _resync_device(self, sender: str) -> None:
+        """We have detected that the device list for the given user may be out
+        of sync, so we try and resync them.
+        """
+
+        try:
+            await self.store.mark_remote_user_device_cache_as_stale(sender)
+
+            # Immediately attempt a resync in the background
+            if self.config.worker_app:
+                await self._user_device_resync(user_id=sender)
+            else:
+                await self._device_list_updater.user_device_resync(sender)
+        except Exception:
+            logger.exception("Failed to resync device for %s", sender)
 
     @log_function
     async def backfill(self, dest, room_id, limit, extremities):