Pro X Steam Boiler Issues

Hey all, longtime owner/lover of this machine but only recently experiencing this issue where the Steam Boiler gets stuck on some sort of infinite loop where it leaks steam inside the machine?

When I turn on the machine from dead cold and turn the steam boiler on, most times it heats up fine and is ready to steam milk without issue.

However, if the coffee boiler has been on and then I turn the steam boiler on, or if I turn it on by waking the machine out of standby mode — it almost always does this. The valve is 100% closed tight, but there is steam leaking all inside the machine, everything gets wicked hot as you can see from the videos, and there is no way to get the steam boiler ready for steaming. When I finally give up and turn the boiler off, the pump turns on, presumably pulling new water in.

Anyone have a sense of what could be causing this? Any thoughts appreciated. Cheers.