It sounds like the issue you are experiencing will have nothing to do with the app you're using. It sounds like either the IR (infrared) signals being sent from your Slingbox are not reaching your cable box properly, or your virtual remote is not properly configured.
This article covers your issue pretty well:
Just in case following this article does not get your channels to change using the Slingbox, here is another article with further troubleshooting for the IR cable:
Hope this helps!
Okay . . . I've been working on this, some progress; I can now change channels, but I've lost a lot of functionality.
I went through the settings on my Slingbox. Everything seemed fine & was correctly listed. I considered doing a hard reset (had already done a soft) so I decided to go through each area of setup & record what was there since it would all be wiped in the hard reset. Again, every setting in there had worked in the past.
Location was fine.
I went to the service provider area and had to make a selection. My zip was already in so I reselected the Comcast Digital that had been in before. The channel line-up was fine, as it's always been. Clicked on next.
This took me to the area for setting up the AV device & it was blank (unlike the type of connection area, which displayed the two types listed and had the correct one selected.)
I went through the AV Device setup and input my DVR, which is a Scientific Atlanta Explorer 8300HD. Slingbox lists this as a cable box . . . it's a DVR (and cablebox of course). I could not find a DVR listing anywhere. Once I selected the correct model, a remote showed up not matching my actual physical remote (my setup in the past always had.) The new "virtual" remote was black instead of silver and lacked any DVR controls. It does at least change channels.
I have lost the ability to control my DVR. I cannot schedule recordings, play a recorded show, delete shows once they are watched, like I could in the past. I can turn on record with the simple buttons at the bottom of the display while watching at slingboc.com. However, the blue menu (start recording, cancel) comes up and stays there. The show displayed does start recording & my DVR does show record, but I cannot turn off recording from my Slingbox remote and cannot access the recorded programs to play.
I have upgraded to a new Slingbox500 connected to Comcast and have basically same problem. I cannot change channel remotely with either the guide, virtual remote or by manually entering the channel number at the bottom RH side of screen.
I only get a constantly changing series of advertisements and weather screens.