Hi Nik,
I was having a discussion elsewhere (a potential new user for RP), and they’d come up with what looks like a new bug, which is no reproducible on my system here – iPad Pro 2020 (iPadOS 15.4, RawPower 3.4.6 (346.01).
If I apply Crop to an image (it may not always happen though) it saves a blank (blacked out) preview image. It’s visible as blank in the filmstrip, and is blank in Photos too. If you remove the Crop, it’s then fine.
I’m also seeing a weird affect on the previews when opening Raw Power for the first launch, the preview opens as a mess of psychedelic colours, selecting another image and then back again clears this.
Cheers
Andy