I do know how to properly make a roux to thicken the gravy.
There's not much to a roux- approximately equal amounts of fat (generally butter) and flour (you can actually use a bit less fat) are cooked together. A small, nostick skillet over low heat works best, but there's a lot of leeway. For a pot pie, you'd probably want a fairly dark roux- peanut butter color or so. Some people insist on adding the liquid hot, others cold; I usually do it hot, in which case it needs to be stirred while and after adding- a flat whisk is great for this. An average gravy uses 2Tb. flour per cup of liquid. You can also thicken it with cornstarch or other starches, which can simply be dissolved in a bit of water and added directly; see the cornstarch box for proportions. There's also a French deal where you make little pills of butter and flour and add them directly to the hot liquid- never done it myself.
p.s. the roux needs to be stirred pretty frequently while cooking.
This article from the site may help you troubleshoot: https://food52.com/blog...
Also, Wondra brand flour is amazing for a recipe like chicken pot pie to thicken the gravy.
Don't use cornstarch if that is what u hv been using. Otherwise maybe your vegetables are too wet and you are not compensating. Good luck! I make pot pies all the time and haven't had a problem. You will catch on.
What happens if you use cornstarch? Too long a cooking time, maybe?