Hi and welcome!!! My name is Sarah and my DS Danny is 3 years 8 months. He is FTT and has several other problems as well including but not limited to food allergies.
I think the feeding teams tips are good ones. If the ball is just now rolling on this that is where we started. Allergies were at the top of our initial list of problems. Food protein intolerances often manifest as GI issues. Food allergies can manifest as congestion and drainage as well...not just hives and rashes. Danny's milk protein issues made him congested, stuffy and EXTREMELY gassy for example. Not the typical food allergy response for not the typical child.

Trust your gut. If you know he isn't growing like he should, push to get the problem solved. It has taken me a little over three years to get us where we are now. Most cases don't take that long but we are finally narrowing things down to a disorder called shwachman-diamond syndrome which even our GI knows pretty much nothing about. That explains the 3 year process.

I would definitely follow what the feeding team is proposing and if they haven't ordered for you to do a food journal with appx portion sizes (tsp, tbsp, cup) for a few days and then submit to the nutritionist then I would suggest that via the phone and they can have you mail one in. The nutritionist will look over everything and if he isn't getting enough calories to pass his body weight then that is likely the cause of his slow weight growth. There will likely be research into why he isn't hungry enough to eat much but at least you would know that he is absorbing things well.
I hope something in there helped.

Stick around and I hope to become familiar with you and your LO's more over the coming months. Feel free to jump right in.