OTB rating and online rating mismatch

I have been playing chess for fairly long time...may be about 25 years.In older days there were no means to play online chess games and casual OTB games were the only means.Since 2013 I have been playing online chess in several popular sites and predominantly chess.com.Other popular sites includes lichess,chess24,chessworld.net and many others.My average rating in all of these sites is around 1700.In some sites its even more.However  when I shifted to fide rated games since december 2015,my performance drops significant and hovers between 1200-1250....with a peak of only 1279!I regularly practice tactics trainer and mostly watch vedios as preparation for tournaments.These vedios include drills and watching master games predominantly on my prefered openings like Queens pawn,modern defence as white and sicilian(mostly dragon and hyper accelerated dragon) as black.Any thoughts on this rating disparity?