Have you run the "enable stacking" after "you configure stacking .... " ?
Also just for everyone information, SummitStack-V do support SFP+ BiDi as show below.
This can saves up on your precious FO core asset.
Generally, all ethernet port status dual LED status as follow.
left LED blinking means theres activity.
left led: Amber means 100Mbps. left led: Green means its 1 Gbps or more.
Right led: Green means port status is active.
If right led green is also...
