SOS when removing USB/Serial from battery powered Xenon

Any idea why a battery powered Xenon with Serial open will crash if you unplug the usb?

Upon restart I see this event: spark/device/last_reset - panic, assert_failed

Here’s a simple program to reproduce:

void setup() {

void loop() {
    Serial.print("millis: ");

@ParticleD, or @mstanley are you able to assist?

I can reproduce that with my 0.9.0 Xenons and Argon too (Boron not yet tested).

If you find a reproducable bug like that it’s always welcome when you file a GitHub issue here

Provide as much background as possible to help reproducing the problem.
In this case for example nothing happens when there is no USB CDC connection open at the time of disconnect but when someone is listening (e.g. particle serial monitor) then the SOS+10 panic occures.
When there was forum discussion about that bug placing a link in the issue description is a good idea too.

Sure, wasn’t clear to me if this was a bug or user error / the nature of the system.

That can be considered a bug since a crash is never a desired outcome and Gen1&2 devices don’t have a problem with it.
So I filed the issue here

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