Dual Memory

I have a Gigabyte Z390 Aorus Pro MB with Corsair Vengeance RGB PRO DDR4 2x8gb 3200MHz.

I put both memory in slots A1/A2, Computer asked me to put in slots B2/A2 which then I did, then reboot.

Now does not boot and beeps, so I have put 1 memory in at a time in each slot all is fine and boots each time.

I then try 2 memory in A1/A2 boots Single Channel.

Then 2 memory in B1/B2 boots Single Channel.

But does not boot in A1/B1 or A2/B2 Dual Channel.

I do not understand what is going on and I not to sure what to do, hope you can help please.