Same here, I get icon randomly:
- on my S5 with Kitkat and SlingPlayer 2.13.1 I get icon everytime after a minute when Chromecast starts
- on my Note 4 after recent upgrade to Marshmallow 6.0.1 and same Slingplayer , the icon usually does not show up unless I enter and then exit settings menu (weird).
- on my wife's phone Nexus 5, the icon shows up everytime, same Slingplayer version. Go figure.
Looks like bug therefore I stopped using Slingplayer icon, instead I use original Google Case app to cast entire screen to my TV and then jut run Slingplayer. No much difference in quality but inability to use the phone for other things while Sling plays. Solved this as well by using dedicated phone (old one) which serves as Slingplayer device.
Like it if it helps. Thanks