I contacted BYUTV online ranting about the same issue and on November 25th, they responded with the following:

"Thanks for reaching out! I’m so sorry you’re having issues with logging in. I’m assuming you watch our channel on Roku? If so I’d recommend uninstalling and reinstalling the channel. This tends to help most of our viewers. Again I’m sorry for the trouble you’re experiencing!"

I haven't had the login problem since following their suggestion to uninstall and reinstall the channel on Roku.  Of course, you would need to sgn in again once it's reinstalled, hopefully for one last time.  It's apparently a defect rather than intended functionality, which would have been insane if it was.  I hope this helps.