1 PCI-E eth. card and one mini-pcie-e card, pci-e eth. prob

When I have r11e-5hnd connected to x86 board and at the same time also ethernet adapter to pci-e , this adapter doesnt work. Only when there is just one pci-e card. System is routeros 5.26.
So I tryed to use 6.9, in this v6 works both pci-e at the same time.
I cant use v6.9 because of instability and mangle and qt problems…

Why I cant have both pci-e devices in motherboard at the same time in Routeros 5.26?