I really feel you on this, it sounds so exhausting and worrying when you can see he is not finishing his feeds. What you are describing with the playing and distraction at the bottle is very common around this age, and the 4-month regression can really throw feeding off for a while. That said, since it has been going on for a few weeks and he is consistently leaving quite a bit, I think it would be good to bring him to see your PD just to rule out anything like reflux or a growth concern, and to get some peace of mind. The PD can also advise the IFC teacher on how to handle the feeds, which might help everyone feel less stressed about it.