I am having an odd issue with my HTC One M8. It shows bars of 4G, but nothing connects, everything from Chrome to Facebook to Spotify just hangs. I have to reboot and usually that reconnects it, but sometimes even the reboot doesn't fix it.
I have an iPad Mini on Verizon, and in the same spot where the One isn't connecting the iPad works fine, so it's not a dead spot issue for Verizon, it appears to be specific to the M8.