I can still get it to go to sleep and not wake up via WKP. As the device falls asleep, the status light goes from light blue > green > dark blue. If I apply motion it just before the dark blue light goes out, it will get stuck.
If you apply motion in this time, the WKP pin is set before the Electron actually goes to sleep, so it can't generate an interrupt to wake it up. I haven't figured out a solution to this beyond using some external component to check for this condition. At least it will wake up after the specified amount of time and reset everything.
If I use a sleep mode other than SLEEP_NETWORK_STANDBY, and it has motion applied to it while going to sleep, it will not wake up with WKP for a timer. It fully crashes until a reset is applied.
There is a bug involving SLEEP_MODE_DEEP and SLEEP_NETWORK_STANDBY that locks up the Electron if the WKP pin is high when sleeping. As far as I know, this has not been resolved. My workout was to just not use these sleep methods 