I can't do anything anymore on the website, I'm constantly being logged out or sometimes shown as the wrong user and most buttons don't work anymore.
Jerboa still lets me use my account but no matter which PC/Laptop/Smartphone I use I can't do anything anymore in a web browser.
The web page at first shows that I'm not logged in, then when I refresh the page, I'm usually logged in but most buttons don't work (eg. clicking on my name in the top right corner doesn't open the context menu - context menus in general don't work). I can't post, upvote, anything. Sometimes, when I refresh the page, it shows me being logged in as a different user as well, but this is gone after another refresh.
Funnily enough I have no problems in Jerboa. Everything works fine there.
I was literally just "logged in" as you on my PC! In trying to figure out WTF was going on, I then was signed in as two other accounts. Ever since the huge increase in users, logging in on my PC has been fickle but never saw another account just the login option. Hopefully it's an easy fix, pretty weird!
Edit: It's now up to 7 different accounts, user interface preferences even. But as soon as I click on anything, I'm fully logged out and see the login option.
I had the same issue after adding a Mastodon link to my bio. I used Jerboa to delete my bio, profile photo, and header photo, and then everything worked fine elsewhere. I’ve since reuploaded my photos and edited my bio without consequences. Your mileage may vary, but doing this fixed it for me.