SFP28 modules not reaching full speed

I have two Mellanox ConnectX-4 Lx Ethernet Adapters. One in my PC, second in NAS. I tried connecting them using SFP28-25G adapters. However, when I connect them, I can only reach 1 Gb/s link. I tried connecting using any of those modules and different 10 Gb/s adapter (same wavelength) and connection was set on 10 Gb/s. I also ruled out cables. What can be the issue?

This is what I get from query:
LinkSpeeds are supported by both device and cable:
1 Gbps
10 Gbps

LinkSpeeds supported by cable only:
1 Gbps
10 Gbps
25 Gbps

LinkSpeeds supported by device only:
1 Gbps
10 Gbps

Looks like the problem is with the PCI-E limit. Is it possible to “remove” one port and use only the second one, so I can reach 25 Gb/s speed?

you can check RN to select compatible module.

https://docs.nvidia.com/networking/display/ConnectX4LxFirmwarev14321010/Firmware+Compatible+Products

can’t remove 2nd port.

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