Do not "sign out" when you close Lightroom use the "quit" function from the Lightroom menu.
I think I understand what is happening.
The service that logs you in automatically is that a system-wide service? Meaning: When I reboot my computer, will some service already try to log on to Adobe Cloud, before a user is logged on?
Because when I log off and back in, I do not have this issue. It only happens when I reboot.
And my user directory is not on my boot drive. It is on an external disk, which in encrypted. When I boot my Mac, I first log into an administrator account with its user directory normally on the boot drive. This will unlock the file vault encrypted external drive. So now I can log in with my real user.
So if some system-wide Adobe Creative Cloud service tries to log on after rebooting, the user directory is not yet available.
Could that be the issue?