I worked around the issue by not updating J! by the Joomla Update component (which activates AkeebaBackup before updating) but simply download the J! update package and process as if it was a new component I installed.
Btw: now I can edit my original ticket, but I cannot unpublish it anymore. Can you pls check and solve the issue. You can remove this ticket for now. Thanks!
Artificial intelligence is no match for natural ignorance...