I have had very simmilar mate, Not sure what it is sometimes, You get into a comfort zone sometimes i think when hitting everything you shoot at then all of a sudden you miss then everything is to blame bar yourself.
Couple of months back 3 foxes were missed in a night 2 by myself and one by a mate, All with my .243. So as you say the rifle was taken to the target and GUESS WHAT ? It was bang on??
Feck Knows the answer, Could be the cold, Bad couple of bullets or the "TWAT" behind the trigger?
EVERYONE MISSES!!