well i was instructed how to properly update which i knew how to but wasn't quite sure about boot-loaders. but what gets me is i flashed the factory image and even on stock with no root, no rom, no kernel i had issues with network dropping, FC'ing apps, random reboots daily, Samsung Knox still causing issues daily (i deleted all apk + odex), only Philz recovery decided to work too TWRP 2.7 4.4 Boot loader edition wont work for anything nothing gets applied at all in that recovery. The only good thing KK has given me is slightly better battery.
YET on 4.3:
Stable, Works, No Samsung Knox issues, Working Recoveries, No network issues, No audio crackling issues
The only reason im still on KitKat is the fact that im waiting for a ROM that will be actually good that's near stock and odexed.
I remember back in my og evo days on one of the forums....that suddenly it arose that many people thought they were doing full wipes and turned out their idea of full wipe meant cache and dalvik.....they didn't realize they needed to wipe system and data......so my point is that there usually tends to be issues based on people's different approaches to upgrading though they swear they followed directions.