Plot hole: Blofeld is played by Telly Savalas. In a previous film, Blofeld had met James Bond and had ordered him killed, yet in OHMSS, when Blofeld meets James Bond, he doesn't recognise him. It's well established over the course of the Bond movies until the reboot with Casino Royale that they all take place in one timeframe, so they should have recognised each other.
Plot hole: Blofeld tells Bond that he realised he was not the real Sir Hilary Bray when Bond told him that the Bleuchamp tombs are in the Augsburg Cathedral. Blofeld informs Bond that they are in-fact in the Saint Anna Kirche, and the real Sir Hilary Bray would've known this. However Bond had gotten his information about the Bleuchamp tombs in Augsburg from the real Sir Hilary Bray earlier in the film.