Assuming they play with sound on the main box have you tried rebooting the mini box, turning the power off to the box wait a minute and then turn back on, if that doesn't work try a factory reset of the box with a mini box you don't have the option to keep your recordings because there aren't any on the mini box but you will need to sign in again to any apps you use.
Don't know why it only happens with some recordings, the program you tested on channel 4 while it was recording did the live version work OK.
