A stalled host enumeration job has been detected

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A stalled host enumeration job has been detected. It has been killed. Please check your A2 for any other stalled jobs or failures as a precaution.

from your A2, this means the A2 found that one or more host enumeration processes was connected to your Xen environment for a long period of time. Typically, this means the XAPI connection is hung. Because a hung XAPI connection likely won't ever complete, the A2 kills them.

As a precaution, it's worthwhile to also check your recent job history for hung backup jobs. It's possible that this environmental XAPI hang can impact jobs, causing them to run for longer or even indefinitely. Simply cancel jobs that have been running abnormally long and re-run them.