So, I created a domain admin but I could never login with that account. I copy-pasted passwords so I was sure it was okay. Then a thought dawned upon me: was the 25 character generated password perhaps too long?
So I changed the password to 16 characters and then everything worked fine!
Now, a feature request: it would be nice if there was an error on both the super-admin page where you create the domain admins, as well as in the domain admin’s “User Settings”, where you can change your password as well. But not when it’s > 24 characters…
At least, it seems to me that way. I have not tested the range between 16 and 25 characters password length.