I am having the same lockup issue which requires removing battery and power on OR plugin power and power on again. It doesn't lockup all the time but once in a while using the camera app or another app like 360 camera (less often lockups).
I read on other forums to try uninstalling some Samsung and/or google apps.. tried these as well no luck. Also, downloaded master cleaner app to clean up cache, temp files, etc. Even reformatted mem card, tried diff mem card, saving cam shots to internal vs mem card, etc.
I even reloaded Kitkat 4.4.4. and my NOTE 4 is still locking up!!!
I love this phone and the awesome pics it takes just it's annoying to restart the phone each time it locksup.