I randomly was looking around at the System Events page for my C-4 and noticed the Zigbee Radio turned off and then back on at around 5:10am this morning. I couldn't see anything in the logs and there doesn't appear to be any elevated load reported at the time (unlike this post). I'm not overly concerned, it didn't cause me any issues and doesn't appear to be a problem now.
There is a great app from @thebearmay to track system resources:
It is very likely that was the same issue as linked. I have also seen my Zigbee radio drop off on occasion on one of my hubs that has a very high resource usage.
Thanks @Sebastien, I've been using the Hub info drivers almost from the start I think, highly recommend them. I have some charts already in Grafana showing temperature, DB size and recent CPU usage. This got me motivated to setup a slightly more detailed dashboard to look at these over a longer period and I couldn't see any issues around that time in terms of CPU, memory, temperature, etc.