MessageBackgroundSyncThread Crashing Strange

Problem :
I have an issue about MessageBackgroundSyncThread, showed up in our crashlytic but we not sure, whats the problem or where the code causing problem.

the issue is happened for 1-2 users, but if happen to user, user can get error like 5-6 times every time he opened the chat room of our apps.

and we are not have steps to reproduce the crash and we don’t have scenario of user impact to the crash

SDK Info
Sendbird Android SDK 3.0.155
Sendbird Sync Manager 1.1.29

Maybe you have some idea what is causing the crash?