I don’t use Beyond, but I should have thought of using the TO state from the tablet… Thanks for the advice, I’ll keep it in mind for the future.
After one session where I painstakingly went through the whole procedure at a very slow pace, double checking everything, and still no dice, I became more and more convinced it was either a bug or some compatibility issue (although I use very few addons), rather than an error on my part. So I just uninstalled the plane completely and re-installed anew.
That seems to have done the trick, I’ve already had two flights since and no issues starting - and keeping - the engines.