Ok so your mining hashrate is pretty stable line, you said you have 4 rx480,'s and judging by the graph each one is mining anywhere from 27-29 mh/s and your expected shares look as they should. both those graphs look perfectly fine. Its just harder to notice the difference because your friend has around 20-25 gpus and the change is more subtle.

If you're having problems with miners shutting off after 20 minutes then that's another issue, im not sure how to help you with that other than to tell you to test each car individually, run it for an hour or more and and see if the problem is isolated to one card or all of them.

one other thing, I believe this line needs to be set to 0 (setx GPU_FORCE_64BIT_PTR 1), not 1, because you are only using 4gb, not more. If you begin to have issues though change it back.