Unfortunately, the error seems to come from OneDrive itself:
DEBUG |20231016 05:42:18|Akeeba\Engine\Postproc\Onedrive::multipartUpload - Got uploadPart Exception 500: cURL error 92: HTTP/2 stream 0 was not closed cleanly: CANCEL (err 8)
This error message says that OneDrive closed the HTTPS connection on their end . Basically, the shut the door on our face and told us not to bother. They did it three times in a row, at which point Akeeba Backup gave up and returned the warning.
So, let's start by making your backup smaller by removing things you should not be backing up. You need to exclude the folder backup
in your site's root. There seems to be more than 8 GiB (!!) of backup archives in there. You definitely don't want to back up the old backups, especially since they are that huge.
Conversely, this will slim down your backup to something around 25 files of 100MiB each (this is a back-of-the-envelope estimate made with the information you gave me) which seems to work fine in your case.
I would also recommend deleting the half-uploaded backup archive files from your OneDrive to make sure you are not hitting your storage limit when you retry the backup.
Nicholas K. Dionysopoulos
Lead Developer and Director
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