hi, I think we had a similar issue ...
with some servers, DAC cable firmware has to be updated,
cause it have to be compliant to a new "standard" ...
it mostly depends on the network interfaces present on the servers ... if they need the "new standard", firmware on DAC cables has to be updated ...
we had this serial that was NOT working
SFP/SFP+ Part Number: 900075-10-02
and this other one that was working
SFP/SFP+ Part Number: 900075-10-03
as you can see,
the only difference is the last number,
that is a sort of "revision reference" ...
when we had the issue,
the ONLY solution was to contact the TAC,
send them ALL the cables for firmware updates,
and get them back ...
let me know