This mod causes a building called "Third Pagoda" to appear for other civs in the tech tree. It also does the same thing and also clear marshes. So I am pretty sure this mod is the one doing it.

Playing a second game allowed me to purchase trade units with faith after founding a religion (playing as a different monsoon civ)

silver and salt on hills in the same city.

have you improved a luxury resource on hills? if you have then there's definitely something going wrong since it's working on my end.

I couldn't buy trade routes with faith.