If you have the chance (and haven’t already done so), can you send a full crash report through the crash report dialog after you did the force-quit? Alternatively, you could paste the last 100 or so lines of the log file (Open Terminal, type open %TMPDIR and press Enter, then open the file aspect-log.sdl in any text editor). It might be that this is caused by the edit variant detection becoming very slow when a large number of new photos gets detected at once, which I also suspect to be the cause of the slow initial scan of the photos folder (Laptop and NAS strategy - #10 by Soenke).