As in, you can type in the password but when you submit it, the login page says it’s the wrong password? Or as in you can’t get the password box to accept foucs? Or as in when it has focus and you press a key, it doesn’t add dots to the box indicating you’ve typed in a character.
The KDE Neon machine I have to use for work does the last of these. But I’ve got two monitors. My workaround is to go log in on the other monitor. And that works, somehow. Weird, and a bit of a pain, but it works for me.
If you meant the first of these, it’s possible you’ve just entered the wrong password enough times that it locked you out for 10-ish minutes.