To resolve the issue, please do the following on the affected server:
- stop the Agent service
- navigate to c:\ProgramData\Apprecovery\MountPoints
- delete everything in that folder
- start Agent service back or reboot the server
To verify that attachability job is working, in the Core console, click on the agent server name, Recovery Points. Click on gearbox drop-down on the right side of the the RP line and select "Force Attachability check"