It has been 2 motherboards already ( or two computers ago) and in those two I have encountered this problem.
Basicaly I buy an expensive motherboard with a capacity of 24 gb of ram but they never detect all of it. For example the other one out of 24 detected 20 ( with a funny bug where sometimes it only detected 12 but after reseting it always dectected the 20). Now my new computer detects 16 out of 24. When it happened to me the first time I sent the board but the new one had it too. After testing all the sticks one by one in all slots I concluded that all were working but for some reason it never detected the 24. What is this?, it has to do with the ram brand?...I'm not sure if it is the brand of the motherboard ( or ram) because so far it has happened in two brands of motherboards and two brands of ram.