I’m going to be following this topic with great interest, because of this:
That’s about when I noticed that one of my Cam Pan v3s began exhibiting the same symptoms. That camera has had a 256 GB SanDisk Extreme card set for continuous recording since I first activated it. The card doesn’t appear to have any problems, as it works as expected if I eject it from the Cam Pan v3 and use it in a Cam v4. Unfortunately, I no longer have date or log information on the card itself, because in my troubleshooting attempts I’ve done a full format with the SD Memory Card Formatter for Linux, so I can’t give a precise date of when it apparently stopped recording to the card.
This is a really interesting observation, I think:
I don’t have any cards that small to try, but after I did the full format and tried the same 256 GB card in the camera, it seemed to record until it showed 7.07 GB used (IIRC; I don’t currently have a card in that camera) when I checked the MicroSD Card screen in the app.
What would cause that limit, and why is it affecting only one of my two Cam Pan v3s? 
I finally got some new cards to try today, but they’re 256 GB SanDisk High Endurance. Hopefully I can do some more troubleshooting on it this week, and I’ll plan to report back what I find and then see if I can get any of the other volunteers to take a look at this.
Thank you for your detailed reporting, @dmorris68!