This is the case where the events were deleted on source because of old event purging and hence min(source event id) > target event id (last replicated event id).
Repl dump should fail in this case so that user can drop the database and bootstrap again.
Cleaner thread is concurrently removing the expired events from NOTIFICATION_LOG table. So, it is necessary to check if the current dump missed any event while dumping. After fetching events in batches, we shall check if it is fetched in contiguous sequence of event id. If it is not in contiguous sequence, then likely some events missed in the dump and hence throw error.