My baby is 3m1w, also on mixed feed.. facing exactly the same issue as you. Sometimes he reject the bottle entirely, sometimes he drink a little bit, fuss and stop drinking but at times he do finish drinking from bottle. I don’t think it’s a teat flow issue as he can finish his milk in 10 mins. Initially I keep latching him as I’m worried he’s not drinking enough (at times he only drink 30ml). But I’ve come to realize one reason he’s rejecting the bottle cause he wasn’t really hungry (I prob mistook his cues as hunger) as he used to drink every 2.5hrs before 3mo, but now he’s only really hungry every 4-5 hrs so I didn’t feed him till then. Though he still drink from bottle now but the amount is much lesser than before (used to be 120ml now max 90ml). I’m not worried though cause he’s still gaining weight and has enough dirty diapers per day.
i have the same problem esp when i bf him more frequent. so now what i do is give the bottle only when he is super hungry. he might not drink all the amount i make so have feed him more regularly. after two three days he starts to be more accepting of bottle.
Maybe change back to the old teat? Some babies don’t like change! Hahah! My niece who is now turning 4, used the smallest teat size till she was about 3. She doesn’t like the new flow teat.
Then just bf? Lesser washing haha