From my observations it seems to be caused by a failure to load & play the ads. So it could in theory happen 2 or 3 times during a whole episode playback. Did you try exiting and re-loading a second time? I know it's a pain! I forgot when answering I watch Neighbours most often on Demand Five which means only one potential ad failure.
Does anyone else have a problem with demand 5 not loading. Takes ages, then says unable to connect. Or if it does load and I watch something it freezes repeatedly. Only have an issue with demand 5, I player and itv player and 4od are fine