Without the proper ER running, UCR does not work correctly. So the ER state must be normal at all times.
Specifically, the Replication Status that can be verified by Real Time Monitoring Tool (RTMT) must be 2 for both the Publisher and Subscriber, as shown in the above link. The Replication Status of RTMT can also be confirmed by show perf query class "Number of Replicates Created and State of Replication".
With ER running normally (the status is 2), the databases are synchronized between the Publisher and the Subscriber of CUC by UCR. Use the show cuc cluster status command to see if UCR is running normally.
If the status of the replications shown below is Connected, it is running normally.
3. Recovering Database Replication 3-1. If the ER Status is "2" but the UCR status is "Dropped" You may be able to recover the Database by executing utils cuc cluster overwritedb on the Subscriber to overwrite the Database from the Publisher to the Subscriber.
Note) Overwriting is completed in a little over five minutes in the laboratory environment where the databases are smaller, but it may take about one hour, depending on the environment. The Subscriber restarts automatically after executing this command.
There will be no effect to the Publisher, but it is recommended to perform this operation in maintenance window or off hours.