I don't have this issue. Connecting to slingplayer with WiFi and LTE both activated always loggin normally. I have had my iphone 5 (Verizon) since November 2012.
My problem is with buffering. Am I alone with this problem? I have the PRO- HD slingbox. My home internet speed is strong, and my computer connection with the slingbox is perfect. But the iphone buffers terribly without the WiFi connection.
I ran speedtest.net on the iphone - Results: download 11.02mbps and upload 3.08MBPS without wifi, download 29.36mbps and upload 7.41mbps with wifi.
Disabling WiFi on the iphone and opening the slingplayer app, the slingplayer streaming rate fluctuates between 80kpbs and 1500kpbs (to view kpbs tap options) I read slingbox support recommended all programs running on the iphone should be closed.Setting should be set for standard quality. I tried both ideas and it made absolutely no difference.
I am very interested to know if your phone buffers and what kpb rate you are experiencing. Any suggestions?