The BBC IPlayer app seems to be working fine on my smart box.
Maybe try going to the My App section, highlight the BBC IPlayer app click on the star * option button on your remote controller and then select remove app. Then go to the App Store on the box, again highlight the BBC IPlayer and press the ok button then click on Add app.
If the above doesn't work then maybe try a forced software update on the box by following the guide instructions linked below.
I have encountered no such problem with BBC iPlayer on my Smart Box ... maybe because I have the latest software installed.
The one change I have noticed is that it now asks me to confirm that I have a TV Licence before it will allow me to watch any BBC content!