I think it's worth doing the extra 2 days, then you know you've done the most you possibly can before you need to refeed.
I'm also sceptical about the mixing thing, but worth a try sticking to exante, especially if you still have stock. I've never used exante so can't really help there and I don't know their makeup. If they are slightly higher in carbs that could explain it. You were mixing them in before if I remember rightly. Do you remember which week/s it was and do you think it affected your loss in those weeks but didn't realise? x x x