Following because I'm having the same issue, except that mine never worked in the first place. At first I assumed I got a bad cable, but now I've tried with 3 different QSFP->4xSFP+ DAC cables (1 Dell branded Amphenol, 2 10GTek), and none of them will link up.
I do see further up in the thread that someone managed to physically break their QSFP ports, and I suppose it's possible that happened to mine before I bought it
on Ebay. But I can see the cables with 'show media' so I don't think that's too likely
The only slightly odd thing I notice is that show media lists the cables as 40gbe, rather than 10gbe breakouts (as I've seen some people's listings in this thread show). Is this normal, or could it possibly be that the cables misidentifying is causing the switch to not try to link up?
telnet@6610-livingroom>show media ethernet 1/2/7
Port 1/2/7:Type : 40GBASE-Passive Copper
Vendor Name: 10Gtek Serial Num: Q191100300070 Revision: 01
telnet@6610-livingroom>show media ethernet 1/2/2
Port 1/2/2:Type : 40GBASE-Passive Copper
Vendor Name: Amphenol Serial Num: CN04Y04W7AG40ME Revision: A