The event that caused connectivity issue around 14:00UTC today was due to a faulty Virtual Chassis link between fpc1 and fpc3.
Instead of dying and re-converging cleanly, it flapped many time.
I'm not aware of any flapping protection for VC ports. Opened T201097 to have better monitoring.
We can also see that fpc1:1/0 shows as up, even though there are no neighbor.
ayounsi@asw2-a-eqiad> show virtual-chassis vc-port fpc1: -------------------------------------------------------------------------- PIC / Port Type ID Trunk Status Speed Neighbor ID Interface 1/0 Configured -1 Up 40000 fpc3: -------------------------------------------------------------------------- PIC / Port Type ID Trunk Status Speed Neighbor ID Interface 1/1 Configured -1 Down 40000
Please replace the link asap.