Hey Stephen,
I had this issue pop up again from here.
viewtopic.php?f=17&t=5816&start=90#p32887This time it was facing a Cisco 3560-X. The Cisco device was acting like a router, no other connections go through it. I had access to the Cisco via a console cable at the time, it did not register any spanning-tree loops or issues. No VLANs were blocked for violations.
The tower feeding port 1 just came back from having the power out.
Sep 22 18:11:37 STP: MSTI0: New root on port 1, root path cost is 80000, root bridge id is 31488.3C-28-6D-5A-A7-83
Sep 22 18:11:37 STP: msti 0 set port 12 to discarding
Sep 22 18:11:39 STP: msti 0 set port 12 to learning
Sep 22 18:11:42 STP: msti 0 set port 12 to discarding
Sep 22 18:11:44 STP: msti 0 set port 12 to learning
Sep 22 18:11:44 STP: msti 0 set port 12 to discarding
Sep 22 18:11:53 STP: msti 0 set port 12 to learning
Sep 22 18:11:56 STP: msti 0 set port 12 to forwarding
<cut>
<this is me flapping the port, no change>
Sep 22 18:24:41 Port: link state changed to 'down' on port 12
Sep 22 18:27:49 Port: link state changed to 'up' (1G) on port 12
Sep 22 18:27:49 STP: msti 0 set port 12 to discarding
Sep 22 18:27:52 STP: msti 0 set port 12 to learning
Sep 22 18:27:52 STP: msti 0 set port 12 to forwarding
Sep 22 18:27:54 STP: msti 0 set port 12 to discarding
Sep 22 18:27:57 STP: msti 0 set port 12 to learning
Sep 22 18:27:58 STP: msti 0 set port 12 to discarding
Sep 22 18:28:03 STP: msti 0 set port 12 to learning
Sep 22 18:28:04 STP: msti 0 set port 12 to discarding
Sep 22 18:28:07 STP: msti 0 set port 12 to learning
Sep 22 18:28:08 STP: msti 0 set port 12 to discarding
Sep 22 18:28:49 STP: msti 0 set port 12 to learning
Sep 22 18:28:50 STP: msti 0 set port 12 to discarding
Sep 22 18:28:55 STP: msti 0 set port 12 to learning
Sep 22 18:28:58 STP: msti 0 set port 12 to discarding
Sep 22 18:29:18 STP: msti 0 set port 12 to learning
Sep 22 18:29:18 STP: msti 0 set port 12 to discarding
Sep 22 18:29:54 STP: msti 0 set port 12 to learning
Sep 22 18:29:57 STP: msti 0 set port 12 to forwarding
Sep 22 18:29:58 STP: msti 0 set port 12 to discarding
Sep 22 18:30:00 STP: msti 0 set port 12 to learning
Sep 22 18:30:00 STP: msti 0 set port 12 to discarding
Sep 22 18:30:15 STP: msti 0 set port 12 to learning
Sep 22 18:30:16 STP: msti 0 set port 12 to discarding
Sep 22 18:30:45 STP: msti 0 set port 12 to learning
Sep 22 18:30:46 STP: msti 0 set port 12 to discarding
<snip>
At this point I got into the Netonix and turned off spanning tree. Things started to pass traffic again. Things were also fine after re-enabling it. I've only seen this so far happening on 1.5.5 and 1.5.6.