i have ADATA 1x 8gb CL16 3000Mhz @ 2666,on my B350 gaming plus with latest BIOS, the XMP profile1: 2666Mhz and Profile2: 2800Mhz.
so i turned XMP off and tryed manually and it worked first try with 0 issues.
i left everything auto, set manual memory Timing ( you find them written on the memory stick) and chose 3200Mhz as speed and worked super great.
Did you set the DRAM Voltage to 1,35V?
I changed the DRAM to 1,35V, set timings manually to the same as XMP Profile (It only shows 1 for 1,2V) and incraesed the frequency from 2666MHz to 2866MHz. It's stable but im worried that im maybe pushing it to far when i increase the frequenzy furthermore without touching the timings...