Trying something new...

Remove all servers from XO and log out.

Host 1 is powered off. On host 2.

xe task-list uuid ( RO) : 727ecb6b-6f2e-15eb-601b-110b2478996b name-label ( RO): name-description ( RO): status ( RO): pending progress ( RO): 0.000 xe task-cancel uuid=727ecb6b-6f2e-15eb-601b-110b2478996b

Task is still there.

From XCP-NG Center. Shutdown all VMs and host2 (All powered off).

Powered up both servers.
Wait 15 minutes to make sure no tasks are pending (xe task-list).

Logging output to file via putty of; tail -f /var/log/audit.log

Added host2 (master) to XO Settings/Servers.

The task hasn't come back.