In a multi-UM environment, it is possible for one of the UMs to become inconsistent with the other. The most likely cause is replication issues. We should document how to rebuild a "bad" UM from a "good" UM. It is currently undocumented:
One of the most common ways to rebuild a MariaDB replication slave is to use Mariabackup:
But as far as I know, Mariabackup does not support MariaDB ColumnStore at all at the moment.