by Ken Task.
The very last step in the entire process is to 'copy' the built .mbz file in moodledata/backup/temp/ to the destination directory (DD). 'copy' on any system takes longer than 'move'. What's the size of the .mbz file that you can see in moodledata/temp/backup/[longcontenthashname]/?
If DD is 'File Area' that's in filedir and for anyone to see that backup in the Moodle UI interface ... and for the DB table mdl_file to know the location of that file, it is important, me thinks, that the progress bar complete and you get a 'success' message.
Check PHP settings for 'time for a script to run' ... default is 30 seconds. If have already tweaked it upwards, bump it up some more.
After tweaking php.ini don't forget to restart the apache service.
Even if you don't need it, think I'd test the backup of that same course to assure it does finish as it should. You can remove that extra backup file after that test.
Also make sure you've turned back on the clean up task related.
Also suggest, if you have done so, installing mysqltuner and checking the DB config to see if it couldn't also be tweaked for better performance.
'spirit of sharing', Ken