En passant is an elegant and legal move played by the players . Mostly, users on chess.com think that it's a glitched move and reports about it as it could be a sort of bug although they're wrong their requests , letters , blogs and forums are reposted by chess.com community it's a fine play .
En passant could be played when the pawn of either black and white are played 2 squares ahead .
For example: If the black pawn is on a4 and white plays it's pawn at b4 then black could legally take it's pawn at b3 . But if black ignores it , it could never take on the pawn again that way and the legality of the move abolishes .
ARIGATTOU