After I dropped my three year old HTC One M8 in a dirty, slushy parking lot at Mt. Bachelor, my phone started jumping into and out of dock mode. This never happened before I dropped it. I waited a couple days to see if the issue would resolve itself but no such luck. The HTC Car app would also start at random. After researching online, I concluded it was a hardware issue. In particular, the USB port on the bottom of the phone was "fouled." Rather than try and clean the port by inserting small objects, I used compressed air. Actually, I didn't have access to my compressor so I built a crude manifold over my vacuum cleaner exhaust outlet and used that to blow out the port. For reference, I don't have a dock for my phone and have no use for dock mode. So that this issue wouldn't resurface, I tried to find a way to disable the phone's dock mode but concluded it can't be done. Happy dialing everyone!
You might have gotten moisture inside the phone. Did you turn off the phone and put it in a sealed bag of uncooked rice and let it sit for a few days to draw out all the moisture before turning it on again?
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.