The karma doesn't change immediately in my experience.
But the FAQ does say some votes aren't counted:
> Roughly, the number of upvotes on their posts minus the number of downvotes. These don't match up exactly. Some votes are dropped by anti-abuse software.
It does if I upvote from the clearnet. I have just done it, and your karma immediately increased by one, from 4297 to 4298.
I use Mullvad.