Electron Deep Sleep Issues

I’m trying to use System.sleep(SLEEP_MODE_DEEP,secinds) on my electron. My end goal is to have the electron wake on a rising signal on the WKP pin or wake up after a long amount of time(6 hours). I thought I had it working, but then I started noticing if I left the WKP pin at high for more than 10 seconds the device would only wake up by pressing the reset button instead of the next rising signal. I’ve tried this on two electrons. Both electrons are 0.6.0. Has anyone else seen this?

void setup()
{
}
void loop()
{
delay(1000);
System.sleep(SLEEP_MODE_DEEP,15);
}