I had this problem last night. The install is moving right along and then halts its progress – just installing the same files or package over and over and over. Pausing/resuming or killing the installer and starting over have no effect – it always stalls on an endless cycle of trying the same files or package endlessly. Doesn’t matter if the “Community” folder is completely empty, as goes the common advice.
My eyes were quick enough to spot the same file name flashing across every time – “Asobo-aircraft-generic-airliner-quadengines”, which turned out to be the clue.
Like a number of folks, the ATC callout “Generic…” grates on my nerves, so I’ve replaced it by modifying the aircraft.cfg file to re-word the ATC callout. Unfortunately, this has to be done in the “Official” folder branch. There’s no override from the “Community” folder structure on this.
Previously, this would just get over-written by any sim update and I’d have to go back and copy my modifications to the “Asobo-aircraft-generic-XXX” types. This time, it appears that the updater only wanted to refresh certain files in the folder, and then must have checksummed the result – which of course would be different due to the modified aircraft.cfg file – and it would get stuck repeating the same operation instead of just blowing away the whole folder and replacing everything with the defaults like it used to.
The solution was to replace the modified files with backups of the Asobo defaults and attempt the update again – then it flew through the install and was ready to go in just a few minutes.
I suspect that if I had no backups, the best solution would have been to just delete the problem folders and their contents and let the updater figure out they were completely missing and then put them back.
TL,DR version: SU9’s updater logic may have a flaw. If you’ve had to modify anything in the “Official” files structure, it may hang because it doesn’t seem to be replacing entire content folders – just parts-- but seems to assume they’ll be otherwise unchanged and may get in a loop when checksums don’t match. Put the default files back to pass the check, or possibly delete entire folders to force a re-download/refresh.