EXTREMELY IMPORTANT: Please attach a ZIP file containing your Akeeba Backup log file in order for us to help you with any backup or restoration issue. If the file is over 10MiB, please upload it on your server and post a link to it.
This site has 6 files >=11.7Mb in size (they are all mp4 files though I doubt that matters). Prior to installing Joomla 4.2.2, Akeeba happily backed the site up as is. After installing the latest Joomla, AKeeba did not like these large files. I had to exclude them to have it complete the backup.
I'm not saying there's anything wrong with Akeeba, but it seems more than a coincidence that the "Backup before update" went flawlessly, then the site updated, and then the backup would not complete. As Akeeba hadn't been updated, I'm guessing somethin gin the latest Joomla version caused this issue.