Fa sho brotherI'm catching hell isolating the problem. I think it is the enhanced search plugin.
Only problem is the enhanced search has been in place since I started using Xenforo in 2015.
Xenforo support still hasn't responded to my trouble ticket and my admin guy can't isolate the problem yet.
I have disabled enhanced search and I'm doing another re-build, we will work the problem until we find an answer.
I'll keep you updated.