Actually…sorry, I’m completely wrong 
The reason it worked for me locally is because it’s been fixed but has not been released. We will get a new release out and things should be all good from there. Sorry about that.
Okay, 2.0.2 has been released of ash_authentication_phoenix with the fix.
Success! That works for me now (the update, I mean). Thank you so much for all your help on this!
