No need for an answer anymore, we figured out the solution.For whoever has the same problem:On Nexus:interface Ethernet1/xx  fec fc-fecOn Catalystinterface TwentyFiveGigE1/0/xx  speed nonegotiate  fec cl74And after these commands, the interfaces came...

I have the same problem: Connecting Nexus 93180YC-FX to C9500-48Y4C using SFP-H25G-CU5M cables.The links do not go UP.Did you managed to find a solution?