Hi @DamienO
As you say you are scanning Hive schemas, this must be putting a lot of load on Hive metastore.
The driver logs suggest there are issues establishing new connections to Metastore.
org.apache.hadoop.hive.ql.metadata.HiveException:java.lang.RuntimeException: Unable to instantiate org.apache.hadoop.hive.ql.metadata.SessionHiveMetaStoreClient:33:1
You could review HS2 logs to see how many concurrent connections were there to the HMS at the time of the issue. Check if there is scope to increase max_connection value in your rdbms, or increase Metastore Heap size to accommodate more number of connections.