Odd Behavior With C9300-48UXM Stack

[brewer789]

I have a stack of three C9300-48UXM switches that connect a number of devices (workstations, servers, printers) using VLANs. After a recent power outage some devices lost network connectivity while others were fine. My first thought was configuration changes not saved and lost after the outage, but I'm the only one with access to the switch and I've made no changes, and there have been multiple previous outages with normal recovery. I noticed that the port activity lights on all the switches blink very rapidly and in unison, which doesn't seem normal. I checked the GUI Dashboard/Switch View and the active ports (with devices attached) are all green and blink in unison at 1-second intervals, which also doesn't seem normal. I expected to see solid green/some amber and no blinking. I've never seen anything quite like this before. I don't see any indications of flapping/errors in the logs, etc. Here's a quick screencast of the blinking pattern:

[Mark Elsen]

  - @brewer789    Verify spanning tree consistency on the switch and or the network; verify if the root bridge is still the intended device (for instance)

   M.

[M02@rt37]

Hello @brewer789 

Please have a look at the front panel — just above the Mode button there are small LED labeled: STAT, DUPLX, SPEED, PoE, STACK..

The one that is lit (solid green) tells you the current mode. What is the current mode now ?