Glad the start-delay removal got that VM going again. I checked and it's a real, documented XCP-ng parameter, "the delay to wait before a call to start up the VM returns", so that explains the behavior.
I couldn't find auto_poweron_delay documented anywhere in the XCP-ng or XO docs, so I'm not sure if it's something XO's advanced VM settings expose under a different name, or something unrelated you picked up while googling.
If you check the VM's Advanced tab in XO and see what's actually set there, that would help pin down which setting you're really dealing with.
Either way this looks like a gap in the autostart guide, since it doesn't mention that start-delay can interact with autostart at all.
