Oh wow, am I glad that I found this suggestion to swap/tighten antennas on my C8!! I have been having sporadic issues with Zigbee ever since I migrated hubs 7 months ago, and have tried so many possible fixes. I fetched my pliers and made the antennas as tight as I could, without wrenching the connectors from the PCB. Within two hours, my most-recent outgage (4 days!) was ended.
Looking back, I must admit I was too cavalier whenever I bumped, and loosened, the antennas. At best, I was just finger-tightening, which apparently is not good enough. This simple solution seems so obvious in hindsight.
Thank you @danabw for the tip, and thank-you @miller.rickm for posting and following through.
