Hey, Andrew,
Glad to hear you can reach your device via UDP after 10 minutes with Hologram. My Particle Electron is consistently deaf by the 3-minute mark or so. (AT&T, southeast Michigan).
Here’s some background (bold is mine):
"About keep-alive
When mobile devices, including phones and the Electron and Boron, connect to the Internet they share a connection through their mobile carrier, similar to how multiple computers in your home share a connection through your home router.
When the device sends data to the Particle cloud, the carrier also opens up a reverse channel to allow the Particle cloud servers to send data back to the device.
(Technically speaking, the device sends UDP data out, and the carrier creates port forwarding to a UDP listening port on the device to get data back.)
These return data channels take up resources on the carrier network, so they like to clean up the unused ones to free up the resources. The Particle SIM has an unusually long timeout of 23 minutes. Most carriers use a timeout of between 30 seconds and several minutes.
When the return channel is freed, the device will continue to breathe cyan, because it doesn’t know that it has occurred. Also, it will still be able to send data to the cloud, so things like Particle.publish will work, and will also restart the return channel if it has been cleaned up."
And this thread, which I participated in back in 2016: