When a recipient failover happens in the middle of tenant oplog application, we might resume applying those donor oplog entries from a point that was already applied due to the fact we first apply the donor oplog entries and then write no-op donor oplog entries for the given batch and we calculate the resume point by finding the latest no-op oplog entry . So, with the stricter mode 'kSecondary', re-applying those donor oplog entries can cause failure and leads to shard merge failure unnecessarily. So, change the tenant oplog application mode to kInitialSync (lenient mode)