Hi, just wanted to let you know I'm having the same issue. I've checked both "Greet New Viewers" and "Greet Returning Viewers", but I've not checked "Group Responses" in either one. I tried to test this out by entering the chat with one of my other Twitch accounts. Upon first time entering he receives the New Viewer Greet as expected. I remove him from the chat and wait until it says "-- has left the channel" before making him enter again. And surely enough the next time he enters he receives the New Viewer Greet instead of the Returning Viewer Greet.
Edit: He does not receive the first time currency more than once.