What model VIC and what cables and what version of UCSM and what model FI?
The 1300 (40Gbps) VIC have a hard time connecting due to "Link Training". Changing the VIC to 40G often allow discovery. See CDET CSCvq21079.
The 1400 (25Gbps) VIC had issues with some cables. See CDET CSCvr04369.
Old UCSM on 6400 FI had issues causing discovery issues. See CDET CSCvo64592.
Those are the few common CDETs from the top of my head.
Could even imagine newer VICs with the wrong "FEC" causing issues, but I haven't personally seen that when connecting to a FI.
Replacing the card doesn't help understand why the links are not staying up (as you have found out).
So let everyone notice that "RMA first" sometimes doesn't fix things.
Could be something on the VIC or something to do with the cables or something on the upstream switch (FI) side.