In the past, I have seen a player that was substituted still playing on the pitch despite that the substitution was done by the game (showed on the highlights page and on comments) , that is, his number and his name labelled on the round thing that represents a player still on the pitch, and he is moving around as if the substitution never happened. If I am not mistaken I reported that on the forum. This season, I noticed it happened at least once.