Solr Shards down for unknown reason

[Dasarathi Minjur]

We have a Hadoop cluster with Solr 6.3 running as service. After an OS
security patching, when the cluster was restarted, Solr Cloud is up but the
shards are down all the time. No specific messages in Solr.log or console
logs. Tried restarting solr but that didn't help. Any pointers to get the
shards up will be helpful. Thanks for taking time to respond.