They have changed the way the tactics get selected. It chooses from a larger range. I've had up to 500 above and below the current rating, though it seems to be heavily weighted on the below side, at least recently.
Original change: https://www.chess.com/blog/News/chess-com-dev-update-april-28-2017
Updates: https://www.chess.com/blog/News/chess-com-dev-update-may-26-2017
Haven't done tactics trainer for a while, but when I recently started doing it again, I keep getting problems rated around 1300. My tactics rating hovers around 1700, so it's kinda annoying not being able to solve harder problems. Is it just me or does it also happen to other people recently?