I’m sorry, I thought I’d posted an update to this – at least I did type something, and it hasn’t appeared here for some reason.
However, for some reason, Raw Power seems to have started working without the issues now. I’ve been editing a few album’s worth of images now, and haven’t seen a single scrambled image during editing. Very weird.
Can’t be sure when it fixed itself, but I occasionally test a few images just to see if the problem persists. So far so good at the moment.
Only a few thoughts and guesses. Could it have simply been an unknown OS bug, that’s got fixed during recent updates (15.6.0 or 15.6.1 perhaps? It was after 15.6.0 I started testing). Could it have been something in Raw Power undetected, maybe accidentally cured in an update? Or how about a rogue app installed on my iPad? I do occasionally cull old apps, or apps I deem not useful at any time. I did have FastestVPN installed (although not active, no idea why I even put that on, as I never intended to use it on the iPad), and have recently deleted it, for example.