Weird RAM/ Mobo interaction

[Yeun7]

Hey guys, so my friend started a new build hes running 

 

i7 9700k

Asus rog strix z390-e gaming

DDR4 16gb tridentz 3000mhz

some m.2

evga ftw3 1080ti

some evga psu

 

So the weird this is how his ram and motherboard is interacting, whenever he puts in his dual channel ram in b2 and a2 (slot 2 and 4) the computer does not boot. Right now he is running the ram in slots 1 and 2, both ram are detected in task manager. Another weird thing is that he able to run single channel, but that single channel only works on the 2nd slot. I have looked at a bunch of random build guides with his same motherboard, and they all run their dual channel memory in slots "2 and 4". Basically im just curious if anyone knows whats going on because im just really curious as to why his is working so differently. 

[Sauron]

The user manual should tell you what the recommended slot configurations for your motherboard are, if they don't work your motherboard might have a defective slot.

[Yeun7]

yes we followed the user manual thats the weird part, following the manual the computer doesnt boot. When he puts it in b1 and b2 it boots then and it also registers as 16gb which is whats weird.