We had to open a TAC case to figure this out. Connected 1/3/9 and 2/3/9 on two sup6t in a vss pair to two separate N9K-93180YC-EX e1/51. Expected them to work and they did not. Replaced with an AOC7M cable and the links came up.
TAC recommended to set speed 40000 on the N9K side.
Interface e1/51
(config-if)#speed?
speed-group Port group speed
Ok can't do that. Now what?
Oh can't configure speed on an interface that is part of a Port-Channel.
Interface Po114
(config-if)#speed?
speed Enter the port speed
(config-if)#speed 40000
(config-if)#show run int po114
interface port-channel14
speed 40000
duplex full
no negotiate auto
(config-if)#show int e1/51 status
Port Name Status Vlan Duplex Speed Type
--------------------------------------------------------------------------------
Eth1/51 To 6807 1/3/9 Connected Trunk Full 40G QSFP-40G-CR4
Thought I would post in the hope of saving others time facing this issue.
