The most common cause of this issue is the infamous "Boot Loop" (welcome to the club). You likely have a piece of hardware on the phone that has failed and has to be fixed or the phone replaced. This is a known problem that LG has "acknowledged" but has not issued an official recall, and Verizon seems to not have any idea what is going and their response is to treat each case as an isolated issue.
You likely have a "bootloop" if you have the following symptoms:
These could be other causes of your issue: