I had to change the Google Play services to the 438 lollipop version because it stayed on the 38 Kit Kat version after the update. Not sure if that happened to anyone else but it caused irratic behaviour.
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How did you know that you had to do this, what was your clue?
How did you know it was the source of the erratic (yes erratic is how it is spelled) behavior?
Apps you can disable which may save battery or prevent Lag
These were found on an un-locked M8, not a carrier version:
Automotive_Traffic
FlexNet (spyware)
Frisbee Contacts
Google Play Games 
Google Play Newsstand
Google+ 
Google Plus for HTC Sense
HTC Account 
HTC DM
HTC Recommend
Instagram for HTC Sense
Kid Mode
Linkedin for HTC Sense
Location Picker
MyGoogleDrive (the one with the HTC logo)
Scribble
Skype (battery hog)
TetheringGuard
Twitter  
Twitter for HTC Sense
UDove more spyware
Zoe (useless)
FlipFont (chinese characters in title)
There is also a Facebook for HTC Sense app that you can't uninstall and 
you also can't disable, even if you never use facebook.  This is a duplicate service, and
if you have ever configured a Facebook account this thing will launch, and you 
have no control over what it does.
(All of the above carry an implied 
Unless you use it clause.
One package that you can't Disable in Settings/Apps is Demoflowpackageinstaller
but it can be disabled in Settings / Security / Apps with Usage Access.  
I have no idea what this is.