Our robotics team purchased two nanos a few months back, and flashed them using the instructions here: https://developer.nvidia.com/embedded/learn/get-started-jetson-nano-devkit#intro.
Both worked flawlessly until today, when one of them started having intermittent boot problems. We are powering them using the recommended adafruit barrel connector power supply with the J48 jumper shorted. On one of our nanos, when we try to boot (on power up or using the J40 buttons), the NVIDIA logo splash screen displays and never goes away. When we use the SD card from this nano on our other one, there are no issues.
[edit]:
I should add that when an SD card unused on the “broken” nano is inserted for the first time, it boots fine and after shutdown will boot to any other SD card (even one that it has frozen on before). Once it freezes it requires a boot cycle with another “clean” SD card. After two boot cycles, a clean SD card will also cause a frozen boot, but will boot fine on our “unbroken” unit.