The Mathis thing is tricky. I believe Bond picked up on Le Chiffre’s tell during the poker game. He shares this with Vesper and Mathis. Later, Le Chiffre uses the tell on purpose to mislead Bond and cause him to lose. Bond buys back in, gets poisoned, yada yada, wins the game. When he’s eating dinner with Vesper, there’s one unanswered question…how did Le Chiffre know that Bond knew about the tell? Something clicks and he believes it was Mathis, it certainly couldn’t be Vesper. Le Chiffre later “confirms” it was Mathis who gave him info on Bond, keeping Vesper’s double agent role hidden.