Using the new SmartThings app, I encountered this the other day during testing. They eventually appeared after about 1 hour. Since you already polled, the application knows this and does not go out and try during a manual add devices.
I went to the main menu (three bars in left of display). Selected the options icon (gear in upper right). Then selected option Auto device discovery as true (blue). Waited a while and the discover occurred. Not exactly the way it should occur, but it worked for me.
The classic app can not auto discover any of the official integration TP-Link devices. But once installed, they work in the classic app.