The Standby ASA5520 started logging the following message sequence for each interface:
(1)%ASA-1-105005: (Primary) Lost Failover communications with mate on interface ________
(2)%ASA-1-105008: (Primary) Testing Interface ________
(3)%ASA-1-105009: (Primary) Testing on interface ________ Passed
This is repeated over and over.
The ASAs appear to be operating OK in spite of the messages.