This isn’t something new, seen it around pretty much any android/sense update since I started doing this. This is just a starting point to finding how to fix it.
Recommended read: Upgrades, what you should do.
Is it a Bug? On a nexus it can actually be a bug, or something that doesn’t do just what it’s meant to to. On a HTC there is rarely bugs, but it happens there as well. When most people have problems it’s rarely/never a bug tho
How can I tell if it’s a bug or not? If you do a factory reset and it’s STILL there and it can be replicated on other phones with the same software number: congrats! you’ve got a bug!
Why do I then have problems? It can simply be apps/etc that doesn’t fully agree with the new update. If you have 245 apps installed, and none of them are from Play store: that might be a small hint. It’s often something small things that causes it, and often very simple: apps installed. Not always though I should point out. Sometimes on carrier/network phones their “additions” can just mess with things a lot. But, it’s still worth it to do a factory reset to just “shake things down”.
So what do I do? I use a 4 step process myself. Or some of them.
1. Soft Reset
Simply press power button (volume up and power button on One M8) for 10 seconds with phone on and active, it will do a countdown after 7 seconds. And will after that do a nice clean restart. This you use if phone crash as well and just doesn’t respond as well.
2. Boot into Safe mode
This is simply boots without loading 3rd party things, perfect if 3rd party keyboards etc doesn’t work. Read about it HERE
3. Wipe Cache partition
A way to get rid of various odd issues with battery etc. Seen it been recommended by HTC. Esp One M7 around 4.4 update. Read about it HERE
4. Factory reset
To simply start over with the phone. This removes all user data and apps installed etc. It will however not revert installed update back to previous version. Just make that you have contacts synced first, as having your contacts on your google account is to recommend. I rarely backup apps etc since they can themselves be the problem. Read about it HERE
Can it be other things? with other fixes? Of course it can be. It’s rarely big complex problems, it’s often the small ones.
You’ve tried ANYTHING you’ve seen and it still doesn’t work? That might be hardware, best to talk with HTC support.