I suppose it’s not the .ini file, but rather the file that follows - probably some big archive that’s being opened (but the display isn’t refreshed before the opening actually succeeds).

Please, try to turn on the creation of the report file in avast! settings and let everything be included there (even the “OK files”). The report file will be rather big, but you should be able to see where the scanner quit - it will be the last (or rather the “one after the last” again) file in the report.
Spontaneous quitting seems like a crash to me… it would be nice to find the problematic file.