I am having the same problem with my S9. No LTE so apps will not work on mobile network. My provider (TextNow) has had me do all the resets and updates. After doing the ##72786# procedure, I had LTE service for four days (Oct 2 thru Oct 6) the back to 3G service. This is very frustrating as this is a documented problem that both Samsung and any providers using Sprint/Boost/Dish network are unable or unwilling to resolve!