I cameback after a year to play the game, and looks like I lost some of the basic skills I learnt before along with some of the achievements. Is this a bug or is it because of the reset?
It's not because of the reset, or you'd have come back to being level 1 with practically nothing. It's probably due to the change over to imagination. Some skills became upgrade cards (which you automatically got), so they don't show up as 'skills' so to speak.