mongo version: 4.0.3

how it happed?
we can hook file write for config server,  oplog will not be written to the file.

1. config server can raise term for election
2. shard server exchange information with config server  and raise lastSeenConfigServerOpTime in memory
3. mongos  exchange information with shard and raise lastSeenConfigServerOpTime in memory
4. restart config server and unregister hook ,  the term for config server lesser than lastSeenConfigServerOpTime