Outlook 2016 blank MFA screen for some users

I have a Conditional Access rule so that when someone connects from outside a trusted IP it requires MFA, I have a few users that get the "Requires password" message come up, they get a window and type in their username and click next, then the window disappears without prompting for MFA and it's back to where they were.

Same thing if they go to File->Accounts if they are signed out and try to sign in they get asked for Email and then it just closes and they are still signed out.

It's not for all users and everyone is using the same Office 365/2016 installation, monthly channel 1903, we use ADFS