iotdb process pretends to be dead and cannot query and write

error reporting during query execution:
may not ready now, please wait and retry later

log_error.log:
2021-12-17 11:50:37,997 [pool-4-IoTDB-Compaction-5] ERROR o.a.i.d.e.c.l.LevelCompactionTsFileManagement:697 - Error occurred in Compaction Merge thread
java.lang.NullPointerException: null
2021-12-17 11:50:48,433 [MergeThread-0] ERROR o.a.i.d.e.m.t.MergeTask:111 - Runtime exception in merge root.benchmark.-1639713043742
java.lang.ClassCastException: null

Start with the compaction errors reported by LevelCompactionTsFileManagement and MergeTask, then investigate how they relate to the query and write failures. Reproduce the reported state if possible; done means the IoTDB process remains available for querying and writing without these compaction exceptions.

Written by the indexing model from the issue text.