OK after much hair pulling the problem was the RAM. I have obtained a different brand/spec (2333 rather than 2400) and it now works fine.
I think you are saying the memory that works is 2133 right. The thing is the CPU will only support 1866 or 2133 without any OC. Yes all memory should run at the default setting at 2133. But we have seen many of these board have problems with fast memory.
Support for DDR4 3333(O.C.) /3300(O.C.) /3200(O.C.) /3000(O.C.) /2800(O.C.) /2666(O.C.) /2400(O.C.) /2133 MHz memory modules.
If people remember that years ago when they started making the CPU's. That all CPU's have a base clock speed. But you could OC to a point & same today. That is the same thing here that memory base clock speed is 2133. Now what they are doing is making memory that you can OC it. By just running it in XMP mode. That has to support that mode too.
The thing is if you do get it to run at the faster speed. Do you really seen any change really
NO. It is like Turbo mode for the CPU. It might show you the the CPU is running faster in the bios. But when in windows what does it run at what windows feel it needs.
What I'm really saying is the MB, CPU, & Memory companies are really pulling the wool over you eyes on this crap. I have been here for 3 yrs. Problems on the Z170 series board it has the worse problem on memory of any thing on this forum. Yes the Z87 boards did have problems too but nothing like this.
Plus Smacker glad you got things running.