I got a friend invite by a user I don't know, and when I went to check their profile I got a blank page. Like, completely white. Is there an issue with the site at the moment, or is it something else I don't know?

Well, that explains it. I do wish people would contact me elsewhere before send friend invites though.

Your privacy settings don't allow non-friends to send you chat messages, though I don't think that's the issue. Getting friend requests from people with no profile that you've never interacted with is just something that happens here.

LOL Welcome to the "land" of Lewis Carroll.

This!
I also received several "friend invites" in the past (and probably will receive more in the future).
Most coming from users, whose names I've never read before in the forum, way less coming from users whose names I know from the forum, and with which I had interactions already on the forum.
But out of principal, I don't accept "friend invites" from anyone who contacts me "out of the blue".