I'm sorry to read thta you are having issues withyour HTC One M8 after the Marshmallow update rldawg. Let's work together to see if we can customize a solution to get the apps working. Since software updates do not remove third party apps, the apps in question will still be on the device after the software update installation. May I ask what app are not working properly?
ArnettH_VZW
Follow us on Twitter @VZWSupport
If my response answered your question please click the "Correct Answer" button under my response. This ensures others can benefit from our conversation. Thanks in advance for your help with this!!