Has anyone seen weird SFP/fiber issues with a Cisco 9300 switch in particular? Weird being link up, seeing packets in/out, spanning-tree good, but no MACs learned, no CDP, etc.

I've never seen anything like this before so I was wondering if any of you have. Off our core 9300-48UXM, one off the SFP ports with a GLC-LH-SMD in the network module just quit working, taking its access switch (2960) down. The weird part is the link status is up and not err-disabled, transceiver details all show signals within range, interface shows packets in and out, CPU was fine, and spanning-tree on both sides shows no blocked ports.

However, CDP on the core switch didn't see the access switch, but the access switch could see the core switch. There were no MACs learned on the core switch, but the access switch was seeing MACs from the core.

Previously we had seen low RX power (-23.5dBm) on the core switch SFP port. Ended up testing the entire run and replaced all SFPs and cables, which we though fixed it when the power went up to -6dBm. Access switch transceiver stats looked fine. Then the exact same problem happened yesterday so in the interest of time, we replaced the access switch with a 9200. The link came up for a minute or two on the core, then went back into the same state described above.

We went back to the core switch side and moved the SFP to another port on the same network module. This time the link came up and stayed up, but the core switch transceiver RX power went back down from -6 to -23.5dBm. I'm not sure what to think in this case and there are so many questions. Why did moving the SFP to another port cause such a drastic loss in RX power on the core switch side? We handled it very gingerly and it was a new cable. Why did the link become stable at low power, but suddenly give up when everything was good at -6dBm? Why was the core not learning MACs when we were clearly seeing packets in/out in the interface counter? Etc, etc. Was hoping someone here has run into something similar and have some insight.