Just hit into a form of this on a 12.5.1 SU3 deployment - this wasn't a new phone add, but a reactivation of a code for an existing phone, the code had expired.
I clicked Generate Activation Code, new code added successfully.
I then accidentally went back and released this code, and immediately generated a new one.
When I exported the activation code list, this is what I saw for the activation code in the spreadsheet:
g?g?-??f-
When I viewed the code on the web page - to my surprise it was exactly the same.
Trying to release that code from the phone page showed the error "phone.activationcode.fail." I had to uncheck the "Require Activation Code for Onboarding" box, save, then recheck and regen a new code for this phone.
Right now there is no workaround listed in the bug, the above should probably be listed. I will investigate moving to a fixed version soon.
