Moto G XT1039: Random reboots to bootloader with "failed to initialize partition table" message
I know that the thread is old but for other people it can help a lot.
I had nearly the same symptoms and i found a reason why my phone dont wanted to start again. In my case it was the battery: https://forums.lenovo.com/t5/MOTO-G-MOTO-G-4G-LTE-1st-Gen/Solution-Moto-G-4g-LTE-random-shutdown-2-4-times-a-day-and-after/td-p/3446925