Interesting. That shows you've tested the cables, and they're ok, so it's not that.
I wonder if the switch(es) themselves have been configured by their last owner to some non-standard settings?
Maybe some kind of weird/unusual port speed combination or similar.
Three thoughts at this point:
- Would you be ok to paste the output of mstflint query command, so we can see any PSID and/or firmware info for one of the cards?
- If you haven't already, look for a way to reset the switch itself to "factory defaults". May or may not exist. No idea, but worth a shot just in case it really is "strange settings have been applied".
- Try forcing the cards to very slow port speeds. Something equivalent to 10Gb/s, and see if that works. Actually, I'd probably try manually forcing the cards to all of the port speeds, one at a time, and see if any of them link up through the switch. Again, just in case the switch isn't negotiating properly for some reason.
Side note - I'm on holiday this week, so likely only limited help from me at this time.
