Yeah, that sounds like a very likely explanation. The good news is that if that is the issue, if you can save it as a rhif file just once -- and then make sure always to work with the layer-remembering rhif, instead of any of the layer-flattening pngs you've already got -- I think that ought to protect your work in progress even when it autosaves due to a force quit. I hope it does, anyway; the current situation sounds so frustrating!