Well reports back from the server engineers was a bit of a dead end. They have continual ping tests and it didn't show up it went down, nor in the server logs. We know the httpd service has stopped as it showed it had stopped, and starting it, it would come to life.
Website can use Apache or Nginx, it was on Apache, so trying the alternative for at least the static files. I'll run some checks. Fingers crossed its an improvement. Also changed some DNS records so its more of a direct route, perhaps a ping test was bouncing off the content delivery network as okay, but wasn't really coming from our web server.