Prime shard closed but cluster was green, but bulk operations failed

I was in the middle of massive delete of the documents (routing was always to the same shard) when I started to get this exception on the bulk operation :
RemoteTransportException[[Jackdaw][inet[/10.0.XX.YY:9300]][indices:data/write/bulk[s]]]; nested: EngineClosedException[[myindex][12] CurrentState[CLOSED] ];

Where cluster was green, replica shard was started and running, and prime shared was marked as started but without any information on what is going on it.
Search on documents placed on that shard was working fine.
What could be an issue here and how can I start this prime shard again.


Is the index open?

Yes, index is open.

The same here, shards get closed without showing anything special, the cluster is green but I cannot index documents. How can I know that something is amiss? What should I do now? Restart the node?

In my case restarting the node solved the issue. But this issue is happening from time to time.