I'd say that it's lost communication with Cayenne, despite the dashboard not showing the yellow "last seen" banner that it typically shows for an offline device. If the gauges aren't updating and the remote commands aren't working either, we've effectively lost communication with it.
Next time you have physical access to it, I'd give it a reboot, and keep an eye on the CPU/RAM consumption over time, it's possible this could be related to the memory leak that we're working on in the Pi agent.
I'm not sure if it's feasible in your situation, but you could, even temporarily, try a wired ethernet connection since you've mentioned weak signal here, just to see if the problem still occurs at all. If it does, you can probably rule out the connection.