I'll give the XMP setting another blast but from what @DarkHorizon472 said above, my particular RAM doesn't appear to play well above 2800MHz (or in my case, even at stock!)
However, according to my motherboard manual, in order to run memory in dual channel mode, I have to use either slots 1 & 2 or 3 & 4 (and I've checked this as I previously tried them in 1 & 3 and CPU-Z reported the memory running in single channel mode!
I would return this memory and try with a new kit that is proved to be compatible with Ryzen chipsets and Ryzen CPUs.