Originally Posted by T4rd
My M8 is on stock ROM, rooted with Xposed and a handful of modules.
Half the time I'm in the Play Store viewing a list of my installed apps, my phone will somehow register a touch anywhere randomly on the display while I'm not touching the screen in any way. Initially I assumed it was a busted digitizer, but it ONLY does this while I'm in the Play Store, from what I've noticed at least. My phone does this while unplugged from any charger/cable.
Also, a lot of times while I'm using the phone while charging, the digitizer will freak the hell out while I'm touching it and register inputs all over the screen and very rapidly. I've seen this on other phones as well while using a crappy non-OEM charger, but this phone seems very much more sensitive to what charger you're using. Chargers that worked fine on my Note 2 and my wife's current GS4 make my M8's digitizer freak out. Has anyone else noticed this?
FYI, I can see these random inputs by enabling "show touches" in the developer options. I'll see touches register on the screen without me touching the phone at all in both of the scenarios above.
Are you using any sort of cases/screen protectors? If so try taking them off and seeing if the issue persists. Also wipe down the screen and get rid of any smudges and fingerprints and see if that fixes it as those can apparently sometimes cause this.
Lastly you can try doing a 'Factory Data Reset' from your recovery such as TWRP, I do not know if the stock recoveries have these but if they do and this is a software issue than this will solve your problem. (Requires S-OFF if it's not available in stock recovery)
If doing the factory data reset does not solve your problem than it is almost definitely a manufacturer defect.
Do take note I did my own research just now to bring you these answers and I am not capable of giving you an overly educated answer like someone else may. Good luck! & I hope the software/case solutions fix it.
Edit: Try disabling Xposed and see if the problem persists too.
VZW HTC One M8 w ViperROM 1.8.0, CheckM8 2.8GHz kernel & TWRP 220.127.116.11 (S-OFF & SuperCID)
Nexus 7 w Cyanogenmod 11