The old caches for the operating system usually get tangled up on bigger updates.
Rooters know to clean those out by hand when changing roms (equivalent of what you all just did) because they can. If you're not rooted, you can't get to all of it. Impossible with any app.
I've written all of the major manufacturers about this and have been ignored - literally a few extra instructions at the end of the installer you received would fix the problem and preserve your data and settings, and I even provided instructions.
If you're not rooted, then your option is to backup everything you can (I recommend Helium Backup), factory data reset (it's the only way to clean up the tangles) and then restore the backup.
You can't back up everything but you can get close. And you have the HTC backup going for you as well.
A lot of people tell me that it's a pain. I can dig it. I resisted it when I first heard of it four and a half years ago (I started with Cupcake lol but didn't get wise to the problem and solution until Froyo).
You can lose your phone, etc etc, so a good backup strategy just makes sense anyway.
You can try this, that and the next thing - snake oil apps are there to take your money - but there's no other solution to get to the stuck bits that are often the problem unless you you are rooted.
People often switch brands over this sort of problem to teach the current manufacturer a lesson and to end the suffering.
None of the makers learn the lesson, it will hit you again on the next big update so the problem isn't going to go away and switching phones is a bigger pain than what I suggest.
Not everyone gets tangled so deeply. Some of you will find the one thing tangled up that you can get to and I salute you in advance. If you're one of those people, congratulate yourself on figuring it out but don't fool yourself that I'm wrong with this advice. Eventually everyone gets a turn at the problem.
If you try this and still have problems that others don't, chances are that the update didn't install properly and then it's time for a trip to your service provider. And 99% of the time to my understanding, they're going to start troubleshooting with a factory data reset.
Sorry - I'm just the messenger.
I wish us all the best luck with the update - I have an M8 myself, rooted, my wife's M8 isn't.
Hope this helps, feel free to disagree, don't let the title mean anything, that's not how we roll here.
