diff --git a/changelog.d/4828.misc b/changelog.d/4828.misc
new file mode 100644
index 0000000000..2fe554884a
--- /dev/null
+++ b/changelog.d/4828.misc
@@ -0,0 +1 @@
+Add some debug logging for device list updates to help with #4828.
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index c09a7c6280..03644a93cc 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -402,6 +402,12 @@ class DeviceHandler(DeviceWorkerHandler):
             user_id, device_ids, list(hosts)
         )
 
+        for device_id in device_ids:
+            logger.debug(
+                "Notifying about update %r/%r, ID: %r", user_id, device_id,
+                position,
+            )
+
         room_ids = yield self.store.get_rooms_for_user(user_id)
 
         yield self.notifier.on_new_event(
@@ -409,7 +415,7 @@ class DeviceHandler(DeviceWorkerHandler):
         )
 
         if hosts:
-            logger.info("Sending device list update notif to: %r", hosts)
+            logger.info("Sending device list update notif for %r to: %r", user_id, hosts)
             for host in hosts:
                 self.federation_sender.send_device_messages(host)
 
@@ -479,15 +485,26 @@ class DeviceListEduUpdater(object):
 
         if get_domain_from_id(user_id) != origin:
             # TODO: Raise?
-            logger.warning("Got device list update edu for %r from %r", user_id, origin)
+            logger.warning(
+                "Got device list update edu for %r/%r from %r",
+                user_id, device_id, origin,
+            )
             return
 
         room_ids = yield self.store.get_rooms_for_user(user_id)
         if not room_ids:
             # We don't share any rooms with this user. Ignore update, as we
             # probably won't get any further updates.
+            logger.warning(
+                "Got device list update edu for %r/%r, but don't share a room",
+                user_id, device_id,
+            )
             return
 
+        logger.debug(
+            "Received device list update for %r/%r", user_id, device_id,
+        )
+
         self._pending_updates.setdefault(user_id, []).append(
             (device_id, stream_id, prev_ids, edu_content)
         )
@@ -505,10 +522,18 @@ class DeviceListEduUpdater(object):
                 # This can happen since we batch updates
                 return
 
+            for device_id, stream_id, prev_ids, content in pending_updates:
+                logger.debug(
+                    "Handling update %r/%r, ID: %r, prev: %r ",
+                    user_id, device_id, stream_id, prev_ids,
+                )
+
             # Given a list of updates we check if we need to resync. This
             # happens if we've missed updates.
             resync = yield self._need_to_do_resync(user_id, pending_updates)
 
+            logger.debug("Need to re-sync devices for %r? %r", user_id, resync)
+
             if resync:
                 # Fetch all devices for the user.
                 origin = get_domain_from_id(user_id)
@@ -561,6 +586,12 @@ class DeviceListEduUpdater(object):
                     )
                     devices = []
 
+                for device in devices:
+                    logger.debug(
+                        "Handling resync update %r/%r, ID: %r",
+                        user_id, device["device_id"], stream_id,
+                    )
+
                 yield self.store.update_remote_device_list_cache(
                     user_id, devices, stream_id,
                 )
@@ -593,6 +624,11 @@ class DeviceListEduUpdater(object):
             user_id
         )
 
+        logger.debug(
+            "Current extremity for %r: %r",
+            user_id, extremity,
+        )
+
         stream_id_in_updates = set()  # stream_ids in updates list
         for _, stream_id, prev_ids, _ in updates:
             if not prev_ids: