Software runs fine on several in-house instances. First time customers hosting it themselves. Runs fine. Users start using. Server need absurdly high processing power and fucks up. I can not access customers Server to debug. Only hope, get copy of their images to reproduce their setup. And have *** one single fucking hour *** to go into it before having to tell in emergency meeting if we can fix it or they would blew the project.

I didn't expect, but found the cause, a single very badly written query. Written by myself years ago I have to admit.
They also gave me one hour to produce a patch. I did but but lost so many hair.