Can you get a feed observed in real life by an IBCLC or a LLL Leader if you have one nearby? 'They could also take a look at the tie for a second opinion. Paeds might not be trained to feel for a posterior tie and you can't usually tell by just looking.
Also, could the reflux meds need a review? He sounds uncomfortable.
Laid back nursing can really help with latch. There is some really useful info here
https://www.laleche.org.uk/positioning-attachment/
