Oplog with incorrect timestamp

One of our mongodb instance shows incorrect oplog info as below:

rs.printReplicationInfo()
configured oplog size: 200000MB
log length start to end: 113778secs (31.61hrs)
oplog first event time: Sun Jan 07 2018 16:05:39 GMT+0800 (CST)
oplog last event time: Mon Jan 08 2018 23:41:57 GMT+0800 (CST)
now: Tue Dec 08 2020 10:11:51 GMT+0800 (CST)

as we can see now is Tue Dec 08 2020 10:11:51 GMT+0800 (CST) ,but oplog last event time is of year 2018,

to confirm that new events is late than 2018, I insert new data, and the re-check, but last event time is still 2018

use hunter_test
switched to db hunter_test

db.myNewCollection1.insertOne( { x: 1 } )
{
“acknowledged” : true,
“insertedId” : ObjectId(“5fceeb33c58ff57252427d4a”)
}
db.myNewCollection1.find()
{ “_id” : ObjectId(“5fceeb33c58ff57252427d4a”), “x” : 1 }
rs.printReplicationInfo()
configured oplog size: 200000MB
log length start to end: 113778secs (31.61hrs)
oplog first event time: Sun Jan 07 2018 16:05:39 GMT+0800 (CST)
oplog last event time: Mon Jan 08 2018 23:41:57 GMT+0800 (CST)
now: Tue Dec 08 2020 10:56:05 GMT+0800 (CST)

what’s wrong with this instance and how to fix?

This node at some point has become disconnected from the replica set. The node was down or disconnected longer than the oplog headroom, and now it cannot recover.

You have to perform an initial sync to get this node back in sync with the cluster…

https://docs.mongodb.com/manual/tutorial/resync-replica-set-member/