We have a MongoDB cluster with the following configuration:

• 3 config servers (replicatesconfig)
• 2 shards (replicaset)
• 3 mongos

After high load testing we found out that the queries start to fail and we get the following error.

ok" : 0,

 "errmsg" : "cannot add session into the cache",

 "code" : 261,

 "codeName" : "TooManyLogicalSessions",

 "operationTime" : Timestamp(1547653301, 1),

  "$clusterTime" : {

    "clusterTime" : Timestamp(1547653301, 1),

    "signature" : {

      "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),

      "keyId" : NumberLong(0)

  }

Inside mongo logs we could find this message:

CONTROL [LogicalSessionCacheRefresh] Failed to refresh session cache: NoProgressMade: no progress was made executing batch write op in config.system.sessions after 5 rounds (0 ops completed in 6 rounds total)

After some research there is no documentation related to this error. What does this error mean? How can we fix it?