I'm among the several ones struggling with AMD GPUs and crossfire (quadfire in my case).
First my Rig :
Motherboard : Asus X99 Rampage V
CPU : Intel i7 5960k
RAM : 32 GB of ADATA DDR4 2800Mhz
GPU : Two watercooled Limited Edition Asus ARESIII (R9 290X2 x2 in Quadfire)
Monitors : x3 24" Samsung 1920x1080 for Eyefinity gaming (5760x1080)
SSD : one NVMe Samsung 950 Pro of 256 GB + 4x OCZ 60GB in RAID 0
Case : Corsair Obsidian 900D
Fans : 16 120mm fans 350rpm - 1350rpm (Corsair, Cougar & Alaska) and one 140mm corsair fan at the rear
PSU : one Corsair AX1200i & one Corsair HX750 for a total of 1950 watts
Watercooling : only the CPU & the 2 GPUs
CPU Block : Watercool HeatKiller Rev3.0 copper
GPUs : Genuine blocks of the ARESIII (I think Asus partnered with EKWB)
Rad : one MO-RA 360 with 9 Alaska Fans
Pumps : two watercool mounted in a 5.25" XSPC reservoir bay
OS : Windows 10 Pro 64 bits
After long weeks of tests and fine tuning, I was finally able to run the quadfire on Win 10 (while only possible on Win 7 before). I checked with MSI Afterburner (to see if the 4 GPUs were loaded during a gaming test) and I benchmarked with 3DMark Fire Storm (scored 24500 if I remember well).
Today, I noticed that only the 2 GPUs of the main card are loaded (crossfire), the 2 others stay flat no matter what application (games or 3Dmark) or what profile (AMD profiles) I chose.
So the crossfire is ok since the 2 GPUs of the 1st card work together but no quadfire.
The only variable I changed is the Drivers that I update every time a new one comes out. One of the mistake I did was to not test again the quadfire after every driver update so now I don't know anymore which drivers were used when the quadfire was working well.
Anyway, today, I'd like to have my quadfire up to speed with the latest drivers but after many tests, trials, attempts, internet researches and forum readings, I cannot have the 4 GPUs working together.
As you can imagine, it is very frustrating to have put so much (time and money) in this rig and to not use 100% of its capacity (when quadfire is ok, I can tell you this rig is a real beast on my 3 monitors !!!).
So today I'm turning to you seeking knowledge, ideas, experiences to fix my issue for good. What I'd like to avoid is the easy solution to sell my cards and to buy a new one (GTX 1080 or Pro duo). I decided to invest in these cards to keep them for a long time. Also, I know it worked a few months ago and I want to fight back my machine and to fix it (I know some of you will understand that feeling... ;-))
So thank you in advance to all of you who will take the time to read this post and try to provide some ideas.
PS : I don't know anymore if it is a hardware issue or a driver issue or a software issue, so I decided to post it in the General Discussions & in the Graphics Forums.