I feel your pain everybody. I spent well over a week going nuts trying to figure out. I am really disappointed in HTC. I went from being a fan who bought 3 HTC phones in 2 years, to wondering whether philosophically they deserve to even be in business.
For those of you looking for the .apk file, I put it them up on this free anonymous file sharing site. But, this crazy android central software will not let me post the links because I don't have more than 10 posts. Yeah I know they want to prevent spam but they also prevent people from helping each other.
Copy and paste one of the two URLs below into a browser tab, but change the first part from h$$ps to https. Someone who has more than 10 posts, please feel free to make them links and post them.
These should be safe to DL and should be impossible for someone else to corrupt/impersonate as long as the links are not changed. To recap, this file came from my HTC One M8. Using WiFi I emailed the file from my M8 to my gmail account, then downloaded to my M9 phone, overwriting the corrupted file that was shipped installed on my phone. I made the zip using the Windows 7 "send to zip file" desktop app. The unzipped file is straight off the M8 as-is, touched only by my phones, gmail and this file-sharing server.
FWIW, those asking about the M7, I don't know for sure. I seem to recall looking for it but not finding this version on that device. My One M7 synced up just fine, so it may have a different app or older app. I will charge it up later and see if I can find any more about it.
Good luck and I hope this helps. Shame on HTC for not making these files accessible to all!