It looks like it's related to the NES app specifically when the NES app tries to phone home to validate your Online subscription, and the WiFi is disabled - it panics and then your Switch crashes.
There's so much shit that needs fixed in the NES app. The fake "burn-in" effect after using the TV filter, the fucked-up color pallets, and now this panic bug... But still no updated version... Hope they fix these bugs in an update or two.It looks like it's related to the NES app specifically when the NES app tries to phone home to validate your Online subscription, and the WiFi is disabled - it panics and then your Switch crashes.
There's also mention of using the power button to force the Switch to sleep with WiFi on also crashing the Switch so the common theme seems to be WiFi related.