Hi Coastobs,
i have the same issues with my nodes. Recently i changed from a laptop to a desktop. Then i wanted deploy a new node, but after a few messages the device stops working. So i checked with a spare mkrfox with the same result.
I have several nodes around and never had a problem, so now im afraid to make firmwareupdates on them.
Enable debugging. Enabling the debugging all the power saving features are disabled and the led indicated as signaling pin (LED_BUILTIN as default) is used during transmission and receive events.
Thank you very much for your help. I was in the same situation in which the code stopped working after the second message package and before everything worked fine. After making the modifications in the library of the link you have sent, it now works perfectly as before.
I will finally stop having this problem that was driving me crazy. Thank you!
"You may note that I switch the Arduino Sigfox library in debug mode. This is basically needed because of a bug in non debugging mode. For real in non debugging mode the SAMD chip is switched to sleep mode waiting for Sigfox communication to terminate. But it never come back from this state. Sound like a bug in the Arduino LowPower library once your have made an USB sketch upload it seems the LowPower.sleep() function never come back."