here is a post from another user:
Hi, everyone, this is my first time here, so bear with me. On Wednesday, August 28, I downloaded the new Kit Kat 4.4.3 update from AT&T onto my One M8. Right after and for a few hours after, everything was in great condition as always. I've had my M8 since launch and haven't had a problem since and hold it very dear to me. Then, after about four hours, I noticed the phone was getting hot, really hot. I had power saver on as always and I saw that the CPU was taxed at 97%, just having Instagram running and YouTube actively showing a video. So I restarted the phone, clearing the cache and making sure that nothing was working too hard. That's when the problems really started coming up. It was getting hot but I ignored it and went to the Play Store to update my banking app and download Reddit News. After seven minutes of a normally one minute (if that) update, I stopped the download, cleared the cache and tried again. Nothing. So Google Play won't download, update, or install apps, Google, or third-party. That's not all. Hangouts will not send messages. Even in full LTE connectivity and 5 GHz Wifi AC, message could not send both to Android users (one used messages, the other Hangouts) and to an iPhone. It was like deja vu with my old iPhone 4S. BUT THAT'S NOT ALL. YouTube was giving me hell, too. When I would type into the search bar to search for a video, the search bar would clear. For example, if I'm looking up and type into the search bar on YouTube "Linus Tech Tips," then it'll work. But if after that I backspace or "x" out "Linus Tech Tips," and type something else, say, "Build a Gaming PC," If I use Swype (Swiftkey, Google Keyboard, or HTC Sense), the first word shows up, but as I'm typing, the subsequent words are erased and "Linus Tech Tips" shows up in the search bar (check him out if you don't already). This is EXTREMELY frustrating and now I can't watch The Joy of Painting. Damn. Finally, the CPU and heat I mentioned before is crazy. The CPU is always between 79% and 99% at all times. the RAM is usually at about 75% as normal, but the CPU is running nuclear hot. It's going to 105-115 degrees Fahrenheit. This worries me, all of this, because I wonder if this is the fault of the new 4.4.3 update for the AT&T M8 model or maybe underlying causes. I've had Malwarebytes scan my phone and find nothing. That caches are cleared and nothing seems to work. If anyone can help I would be extremely grateful because my only option in my mind is to do a hard factory reset of the device. Thanks to anoye who can help, and if not, then, oh well. Thanks, and sorry I made an essay out of this, this is really a big problem for me.