Java (JVM) Heap allocation is not sufficient to support FglAM and agent operation. As a result, the DBSS agent(s) are not able to upgrade and are unable to connect to the instance due to driver mismatch.
Agent Manager is down, decommissioned or inaccessible while trying to Validate a DB agent connection.
1. Increase the JVM heap per the Cartridge Hardware Sizing document recommendation
2. Restart the Foglight Agent Manager
3. Run the DBSS Installer wizar and configure monitoring agents to upgrade and operate normally.
Reinstall the the Agent Manager if required, and delete and redeploy the DB agent(possibly to another existing FglAM).