I'll join the fray here as I'm seeing some odd behavior out of my Nitro+ this week.    I got the card last week, flashed the rom and was pleasantly surprised to see the hash rate get up to around 31 MH/s so I let it alone and went on my way.  Fast forward a week and this card is unable to get over 18.75 MH/s, at some point along the way it just dropped down there and stays there.   It's set to compute mode but the crazy thing is that when I set it to graphics mode and reboot the hash doesn't drop at all, it just stays at 18.5 -18.77 MH/s.  I switch it back to compute, reboot and it's at the same rate.  I've flashed back to the original rom and sure enough the hash rate stays exactly the same, 18.5 - 18.75.  Flash back to the rom that got me up to 31 MH/s and the results are the same, 18.5 - 18.75 MH/s.

Running on a B250 Mining Expert with 6 other 570's, 3 gpu's on one PSU, 4 on another with power to spare.  8GB of dd4 ram, a 64GB swap file sitting on a nice fast SSD, all powered by an intel 4400 cpu.  Would love some advice if anyone has any