Had the same thing. I know the steps to clear it but still can't figure out what causes it and why it's happening so randomly. Keep me posted, I'll get it soon.
Ok, I tried disabling another feature that seems to have something to do with this problem. Let me know how things are from here onward as well as if some functionality became lost.
Sorry... I think I narrowed down the source code in question but still not completely sure how to tackle it. I also determined what feature gets disabled. I'm doing my best to resolve this.
Ok, my troubleshooting seemed to point me to the user banning system which doesn't surprise me. I have literally banned thousands of spammers. It might been just that the list was overflowing so I erased it. Before you gasp and worry, I transferred the entire list of known spammer IPs to the firewall to continue blocking. So hopefully now things will run smoother with a freshly started ban list.
So let me know if things are still problematic or if the problems are all gone starting today.