Hm, the app shouldn’t crash - given you are previewing large RAW files I assume this is some kind of memory limit thing. Please run the TestFlight build and be sure to send the crash report whenever it occurs. This way I can see what’s going wrong.
The app currently doesn’t generate thumbnails for files on viewing, because that (depending on the file type) could require two requests for the file (one from e.g. web view or video streamer and one from the thumbnail generator) which may be undesirable (when e.g. on rated connections).
I will consider on-demand thumbnail downloading from a (shared) thumbnail folder.