[OnePlus 2 Q&A, Help & Troubleshooting] N2A:
I've been given an OP2 64GB as a project from a friend to try and return to stock and working. It was running a custom ROM which wasn't working particularly well, so I did the full reload to stock 3.0.2 via the Qualcomm download described here by [MENTION=4844194]fareed_xtreme[/MENTION] which downloaded okay, booted up, and the touchscreen seemingly didn't work. I've come across that before where there's been driver or firmware mismatches, but then I realised that if I held my finger on the screen for between 2 and 4 seconds, it'd start responding, right up until I let my fingers up off the screen. I could do multiple scrolls by adding a second finger to the mix, and it'd keep responding until I let go, at which point I'd have to hold down for another 2-4 seconds to make it do anything. The digitiser is fine, I enabled the overlays in dev tools (painfully clicking item by item!), and it shows the traces fine. They don't show up at all as screen presses until said delay happens, which is very odd. It also responded fine in the recovery, which was plain odd.

After a while, I tried returning it to 2.2.0 courtesy of [MENTION=4844194]fareed_xtreme[/MENTION]'s other guide, which then worked fine, booted up, had 2.2.0 installed, touchscreen worked fine. Did notice the baseband version claimed it was unknown, though I'm unsure if this was related to me having no SIMs in it. It did initially offer me an OTA upgrade to the latest Marshmallow, which I allowed it to do, and promptly had the same issues again.

I've tried flashing various ROMs - Resurrection Remix etc, to find they've got the same problem. Any Marshmallow-based ROM seems to suffer from this weird input lag. The capacitive buttons are fine, it's just the display. Also, weirdly, it works if I touch the screen just as I wake the phone with the power button - so I can hit the power button and immediately swipe the lockscreen off, but then it reverts to the previous behaviour.

I've tried re-flashing the firmware for the various ROMs (matching with the installed ROM obviously). I've also repeatedly wiped the system/data/cache partitions etc, and have backups of EFS via TWRP saved off the phone. I also spotted two threads on the OnePlus forums describing this exact issue here and here, both with no solution. I also noticed people have had similar issues long ago when they tried installing H2OS and then returning to stock, without doing the full qualcomm download, but they seemed to be mostly solved with the full ROM reload and a cache wipe.

My next step is to flash back to 2.2.0, and incrementally upgrade with the OTAs, see if it works, but I suspect the second I make the jump to 3.0.2, I'll lose the touchscreen again. I've left it OEM unlocked, and got TWRP and original recoveries available.

To be honest, worst case, I just reflash the phone back to the final 2.x version, at least it actually works then, but... I'd really love to know why I can't fix this, and what the actual issue is, if anyone out there knows. There doesn't seem to be much on here in the way of people experiencing the issue - either that, or my search-fu has repeatedly failed me. My gut feeling is something kernel/driver related, but I don't understand why it wouldn't get fixed with the full firmware download via QC.

Help me, XDA, you're my only hope! :confused: