The issue is observable only in v3.6 the BACKPORT-1861 made the absence of keys apparent as the clusterTime was removed from the metadata (before there was a dummy signature)

The problem happens in an ReplicaSet started with shardsvr:true and later added to a sharded cluster or in a ShardingTest with auth

The KeysCollectionManager starts the monitoring thread when the RS is aded to a cluster and does not make initial refresh but eventually refreshing within 30 seconds (default refresh interval)