Failed – No file despite backing up

Up to today I had no problem with the plugin (using the premium for restoring for years).
Today – after downloading a backup that was successfully created three months ago – I am unable to download a newly created one. The creation takes much less time than usual, the download button is greyed out, attempts to save it returns “Failed – No file”.
There is no .wpress backup file in the ai1wm-backups folder anyway (despite claiming a 750MB file being created)!
Plugins are at the latest versions, php is 8.0.
Space is plenty, memory is 512MB, file permissions 755.

Not sure what else I can check…?

Thanks!