Display dims, corrected by twisting the case?

Was recently issued a new HTC One M8 (windows os) and initially thought the phone was a POS because the display looked awful. After using it for a couple of days, I discovered the display was very dark BUT improved if I gave the phone a bit of a "twist". I would just go back and get another one but I have invested a lot of time into setting the device up and since it is issued from work, I can't just go to Verizon and have them clone the phone over to a new handset (if they even could).

Obviously this indicates to me a loose connection but would appreciate a little advice on the most likely culprits before diving into it.

Also wondering if this is a common issue with the M8. Nothing found searching the web so I wanted to pose the question to the experts here!

Thanks, Allen.