Slow Drinker

Hi Mummas! I was wondering if anyone else has found that their 6 month old has started taking their sweet time to finish their bottles? Normally it would take 10ish minutes but now it’s taking anywhere between 25-30 mins! And he hasn’t even finished the whole bottle by the end of it? We use anti reflux milk and are on the maximum teat (X vari flow teat) for mam bottles. I don’t understand what’s happening