Exception in server tick loop Crash after enable MythicMobs for a while

Recently my server crash frequently with totally same error. I have tried making experiments to test which plugin causes the crash. I used the Plugman plugin to disable or enable several plugins, and I found that after enable Mythic Mobs for 50 minutes, the server crash. Disabling MM will solve the problem. The weird thing is, the server is not crashing. It just like someone typing /stop, and all player data stored. The console said


And I also uploaded the crash report below. My guess is...

Exception in server tick loop Crash after enable MythicMobs for a while