I just purchased the new HTC M8 phone and love it but it keeps rebooting at least 5-6 times a day. I have been on the phone with HTC and they told me to do a hard reset which I did and it still reboots. Since the phone is only 3 days old I went back to Verizon and they replaced the phone but this morning it rebooted again so it is not hardware. I do have a scandisk memory card in it and took that out and it still rebooted. So I did a factory rest again for the 5 time and did not install any apps at all and just the phone with my work and personal email installed and the phone is still rebooting. Unfortunately I really like the phone and do not want to just give it back and get a new one so I would like to know if there is anyone having the same issues or not.
It has something to do with the device/software itself. I have an Lumia Icon with Windows Phone 8.1 Update 1 (same as the HTC) and no reboot issues at all.
Do another hard reset and don't setup any mail accounts and see if the phone still reboots. Wonder if there is problem with either your personal or work accounts causing the phone to reboot.
If the phone still reboots I would continue to contact HTC support instead of VZW on this and let them know that even the replacement is rebooting.