My FIL often has efficiency issues with his AiO system and a friend of mine had similar issues to the point where he built himself a cooler mash tun to use with his. I don’t know what the issue is, but you can pretty easily solve it by purchasing an extra pound of base malt for a few bucks. At the homebrew scale this isn’t breaking the bank (like it would be a commercial brewery making 100s of bbls).