Thanks for the reply. Yep, understood re weather failures. As previously mentioned, the help file states, "A failed Plan can be automatically rescheduled to run again in the same or another night."
Can you point me to that? I think it is a holdover from the very old days before it became apparent that this was a bad idea.

Please submit a couple of ACP Run Logs that are from those failed plans. I think you are using the web UI? If so in the Schedule Browser table list, drill down to the Observation that failed and see if you see a link leading to the log. If you are not logging in with a username/password ("Use Web Browser" button, user Observatory Operator) then these logs are in My Documents\ACP Astronomy\Logs\Scheduler\ddddmmyy\...