Facebook and many other properties put their effort into the phone apps. The regular website from a browser is almost always an afterthought. I don’t use FB but use instagram and the website itself is awful, half the crap doesn’t work.
If it usually works for you, I’d imagine some bad code was pushed to production and may or may not be addressed.
These types of sites generally prefer their users to use the apps as it’s easier to exfiltrate your data.
Edit: you can try and dump your cache, delete cookies, etc. to see if that helps.
