A blue responded to a thread about this issue in the customer support forums and confirmed that there were multiple people reporting the same thing, so they’re at least aware of it.
Seems like a pretty big issue for there to not be more uproar about though. It resolved for my friend, but there are clearly people who just can’t queue for specific dungeons at all, almost a week later.
I’m gonna recommend voicing your issues over in the customer support thread as well, probably more appropriate and higher chance of being seen since a Blue has posted:
https://us.forums.blizzard.com/en/wow/t/role-unavailable-in-specific-dungeons-cue/688282