I have a private set where I put all posts that I want to find the source of.

When I've found the source of a post, I remove it from the set.
The problem is that very often, e621 just displays the message "Removing from set..." and then gets stuck.
Reloading the page confirms that the post has indeed not been removed from the set.

I'm no database expert, but surely removing a post from a list can't be that resource-intensive?

The site was running really slow last night, maybe that was the problem. Otherwise it usually works fine in a second or two for me.