Couchbase web console error & cpu load high when rebalance & rebalance failed

We have a Couchbase cluster of 5 servers, all with CE version 4.1.0, and after one server failover,

  1. we get no info after logging in the rest 4 servers’ web console.It looks like this.

    some url like returned status code of 500,
    and such info [“Unexpected server error, request logged.”]

  2. So we add several servers into the cluster, the new added servers’ web console works.

3.And we rebalance the cluster, removing the old 4 servers. Things happened, the CPU LOAD of the old 4 servers became too high, accessing about 40 to 50, and the old 4 servers became pending, and the rebalance failed.
4.The logs says

[user:info,2019-06-17T16:55:47.164+08:00,ns_1@<0.20265.1924>:ns_orchestrator:handle_info:493]Rebalance exited with reason {timeout,


{none,<<"Rebalance stopped by janitor.">>}]},

I wonder who is the guy janitor? Why did he stop our rebalance?
5.When the CPU LOAD raise, I found there are many beam.smp with the status of top Dsl. Does the dead beam.smp raise the cpu load?

Any help would be appreciated.