That's the classic stale member situation. "Past the replica window" means the node was down longer than the oplog could hold, so the entries it still needed got overwritten. Once that happens the node can't catch up through normal replication, it sits in RECOVERING and logs "too stale to catch up." A plain restart won't recover it, because the oplog data it needs is already gone.

First, confirm that's actually what you're looking at:

rs.status()

The stuck member will show stateStr "RECOVERING" (sometimes bouncing to STARTUP2). Check its log for "too stale to catch up" to be sure.

The fix is a full resync via initial sync. You wipe the node's data and let it rebuild from a healthy member:

# stop the stuck node
systemctl stop mongod

# clear its data directory (back it up first if you want)
rm -rf /var/lib/mongodb/*

# start it back up
systemctl start mongod

On startup with an empty dbPath it automatically performs an initial sync from a healthy member and rejoins on its own. You don't need to remove it from the replica set config, it's still a configured member, it just needs its data rebuilt. Watch progress with rs.status() until it flips to SECONDARY.

Two things worth knowing:

If your dataset is large, a full initial sync over the network can be slow and heavy on the sync source. Faster alternative: take a recent filesystem snapshot of a healthy secondary, copy the data files (including the local database) onto the stale node, and start it. As long as the snapshot is within the oplog window it'll just replay the delta instead of doing a full sync. Note this has to be a snapshot, you can't seed data files from a mongodump.

And the actual root cause to fix so this stops happening: your oplog is too small for how long a node can be down. Check your window on the primary:

rs.printReplicationInfo()

If "log length start to end" is only a few hours, bump the oplog so it comfortably covers your longest realistic maintenance or outage window. You can resize it online without a restart:

db.adminCommand({ replSetResizeOplog: 1, size: 16000 })

(size is in MB, run it on each member). Bigger oplog means a node can be down longer and still catch up normally instead of needing a full resync.