For whatever reason, the site doesn't keep me logged in.

[Kyasarin]

If I'm inactive on this site for a short while, I always end up being logged out. This has started happening since Wednesday and never happened beforehand.
Before you ask: Cookies are enabled and I do not have them cleared frequently/automatically.

Does anybody know the cause of this, or how to solve it?

 

[Cue]

The 3.8.5 update messed with the hash, anyone who had a cookie cannot logout properly and anyone who didn't cannot stay logged in.

Solution for both not being able to stay logged in and not being able to stay logged out: Kill all cookies for this site (or all if your browser doesn't allow for single site cookie deletion) then login again.