Mysql connector with snapshot.mode=schema_only. When the source mysql server is idle debezium performes schema snapshot, but doesn't store binlog offset as this happens only when data is produced. For idle server there's no data changes = no offset.

Now after debezium instance restart or rebalance event the restarted task state machine goes into wrong path thinking it's new job and starts to perform another schema snapshot. This leads to ever growing history topic.

Some ideas:
Send one heartbeat when snapshot completes - this will trigger offset storage.
Send offset periodically by time trigger.