MM2 can sync offsets only when the consumer group is not in use in the target cluster. If it is, offset synchronization cannot be done. However, the error message isa bit confusing talking about UNKNOWN_MEMBER_ID instead of about consumer group being in use.

We should investigate if the error message can be somehow improved to make the logs more useful and readable.

At this point, it is not clear if it will be possible or not to improve the error message.