Debugging balancer? How to safely stop all in-prog migrations?

mongos> sh.isBalancerRunning()

mongos> sh.getBalancerState()

I have stopped the balancer but it seems to be processing a very long-standing migration. How can I see the status of this migration? How can i force-stop all migrations safely?

Also what is the impact of trying to index a populated, sharded, collection while the balancer is enabled/running? Is this safe? I ask because I attempted to build indexes on a few sharded very large sharded collections in the cluster but noticed one of the shard nodes did not completely build all the indexes when I ssh’d into it and checked. This node in particular kept repeatedly trying to build a fulltext index over the span of a few days, with this message in it’s mongod.log

“Restarting index build”

My sharded cluster is running 4.4 community edition on AWS graviton r6g (ARM) servers

Follow up – any advice?