I got Asus Prime H270 Plus with 2x PCIEX16 Slots. But only the first slot gives me 26mhs, the second 16x slot is not working as the other. Tried swapping out GPUs to see if it's due to the GPU but not.
I already have enabled Gen3 + 4g decoding in Bios.. Not sure what to do :/
Did a quick google search on your mobo, it seems like the second 16x slot is only able to handle x4 mode which explains why the second 16x slot is slower.
Same thing with my rig. One GPU is hashing 28 MH/s, second GPU is hashing around 20 MH/s and they are both directly connected to the mobo.