It does have a lid on it. It boils water underneath so I’m assuming the lid helps keep steam in to heat the milk
Maybe try to heat it without the lid and see what happens! Ours does the same and they warm up nicely. That way you don’t have to get a new warmer or worry about water getting in the bottle
I have the same bottles and mine don’t fit in the warmer either, what I do is just put the lid on top of it anyways 🙂↕️ or I sometimes take the nipple out. It doesn’t really make a difference to me. It still warms up
Do you have to have the bottle warmer lid on? I have the Dr. Browns bottle warmer and it’s just an open top. TBH I got it second hand so it might have come with a lid but I don’t have one.