I am also having the same problem - I can no longer stream from my ipad mini or my ipad air or iphone 6 - I also just get sligplayer disconected message - This is a real issue as I only bought the slingbox so I could stream my home cable to my tv in my work temporary apartment.
Why is the slingbox team not answering these issues in a timely manner - I see many postings with no response
This issue still exists in iOS9 beta.
I also have El Capitan installed and airplay works fairly well. It's only when I switch to my iPhone 6 plus or my 1st gen iPad mini (both iOS9 beta) that the struggle begins.
I can often get it working by turning airplay on first, sliding the switch to turn on mirroring, and then turning on app I want to airplay. Sometimes I have to play with a bit by turning mirroring on and off a few times.
The problem is I would prefer not to use mirroring, it changes how video is displayed on my TV. Without mirroring I use the entire screen on my TV, not so with it on. Now sometimes I can switch mirroring off and it will work, but it's touch and go, and often what happens is that it will start "stuttering" like it's constantly stopping and starting. Thats when I switch back to mirroring.
There is an issue with the Slingbox App. For the past three days on all of my apple devices I have been un-able to airplay. Each time I choose to connect via airplay, the sling box disconnects. I have to restart the app and I try again and it gives me the exact same error. I have never had this issue. I am running the most recent software for sling box, sling box app and apple iOs software. Any assistance would be much appreciate. Thank you.