I’m getting the same with a fresh install of Manjaro. When I lock the screen manually and quickly unlock it, everything works fine. But if the screen locks due to a timeout, it switches to a dvorak keyboard layout, which trips up my password entry (since I have a y in my password which is now in the z position). I can confirm this by bringing up the virtual keyboard, which reflects the dvorak layout.
I don’t use dvorak. I only have EN-UK installed as a locale. I have no idea what’s happening here.
Even more infuriating, Manjaro appears to be configured to lock the account after 3 failed login attempts. Not sure what the point of that is on a single-user system, but I had to edit /etc/security/faillock.conf to bump this up to 3000 so it doesn’t affect me (see: Account gets locked for 10 minutes after 3 failed attempts).
Edit: just to add, there’s no fingerprint reader involved here. My PC is an off-the-shelf desktop unit.
Edit2: Seems to be affecting a few folk, although this link is also fingerprint related: Getting locked out for "3 incorrect attemts" even though there were 2 and the password was correct