diff --git a/changelog.d/3606.misc b/changelog.d/3606.misc
new file mode 100644
index 000000000..f0137766a
--- /dev/null
+++ b/changelog.d/3606.misc
@@ -0,0 +1 @@
+Fix some random logcontext leaks.
\ No newline at end of file
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 1d41d8d44..44f37b4c1 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -311,6 +311,12 @@ class SQLBaseStore(object):
         after_callbacks = []
         exception_callbacks = []
 
+        if LoggingContext.current_context() == LoggingContext.sentinel:
+            logger.warn(
+                "Starting db txn '%s' from sentinel context",
+                desc,
+            )
+
         try:
             result = yield self.runWithConnection(
                 self._new_transaction,
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 906a40503..ee9e4d4b6 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -142,15 +142,14 @@ class _EventPeristenceQueue(object):
             try:
                 queue = self._get_drainining_queue(room_id)
                 for item in queue:
-                    # handle_queue_loop runs in the sentinel logcontext, so
-                    # there is no need to preserve_fn when running the
-                    # callbacks on the deferred.
                     try:
                         ret = yield per_item_callback(item)
+                    except Exception:
+                        with PreserveLoggingContext():
+                            item.deferred.errback()
+                    else:
                         with PreserveLoggingContext():
                             item.deferred.callback(ret)
-                    except Exception:
-                        item.deferred.errback()
             finally:
                 queue = self._event_persist_queues.pop(room_id, None)
                 if queue: