The base path here is absolutely identical and has not been changed.
In this path is as said no folder with the domain created at that time. What amazes me is that despite the missing folder yesterday in this path exactly this domain could not be added.
Today I tried again and it worked. I have no idea why and could not reproduce it.
The only thing I did in the meantime was to add another domain and deleted it again today, before now capturing the origin domain.
Curiously, the folder with the archive and an e-mail from the domain that was automatically deleted at the time is still there - see date. That was the only mail I had sent myself and was archived yesterday, before I ran the update to the current beta.
Important maybe this has a connection: I have the first beta version with a test license, the other beta version 8291 without LICENSE had installed and this beta version with license.