Before moving ahead with the below, please ensure that the HA Cluster is in a healthy state, and that a current backup has been stored separately from the appliance in the event it is required as a precaution.
In order to clear this error, please try one of these options:
1. Reboot the Replica.
2. Move the Replica to 'Primary' mode via the Primary 'HA Config' screen. Then please follow the steps in this KB article to re-establish communication between the Primary and Replica:
"How to re-establish the HA pair."