Thanks, @sam, that is very helpful. Now I better understand why a plugin (which is making too many ajax calls) could be causing the problems we are seeing on our site. Besides the “extreme load” message, we are also seeing white “slow down” screens (too many requests, nginx), which would also fit into the picture.
We are now in the process to identify the culprit. One problem we already found is Babble. Our chat was well over 10k posts, which was causing heavy load on the system:
I’ll report back once we know more.