There is a problem with Pandora and the S6. You can get it to work, if you immediately minimize it after starting it, and ignore the WAIT-CLOSE popup. It continues to work, but sometimes it will not respond to bluetooth next-track button presses. I have been waiting for the app to update, figured they would quickly resolve a problem with the latest Galaxy phone, but here we are still.
This is not the first device that I have had that Pandora had trouble with until an update comes along to fix it, but this is the longest I have waited. I have instead been trying out the new Google Play music station stuff that is very similar, just not nearly as well trained as Pandora after years of thumpup and thumbdown entering.