"password incorrect" after update

Hello. After installing the latest update today I’ve been having some serious problems. The first thing that I noticed was that immediately after the update was complete, some of the text Iwas typing into Firefox looked “corrupted”, like some of the characters didn’t show up properly. I then went to restart my system to complete the update but it gave me an error message. The message may have said something about " session manager" but unfortunately the restart went ahead before I had time to read it properly.

It’s after this restart that the real problems have begun. I am now unable to login because my password is considered incorrect. One solution I found suggested booting in rescue mode, going to /etc/pam.d and merging ‘system-auth’ and ‘system-auth.pacnew’, but I only have a ‘system-auth’ file so that doesn’t seem to be the issue. I’ve also tried using init=/bin/bash to change my password, and while I could change it I still get ‘password incorrect’, even with this new password.

Is there any way out of this? I’m completely lost at the moment.

EDIT: After some further digging I’ve found that the /etc folder does contain some .pacnew files. Notably ‘shadow.pacnew’ only contains the root user and not my usual user. Could this be the issue?