You can check the TV signal and quality for the channel by:
Pressing theHome(or YouView) button
Going toSettings >Signal & Connection >TV Signal Quality
If the signal quality is less than 50%, this indicates that your signal is too weak to receive this channel. If you're signal is too high, this could also cause the issue. You could try connecting your set top box to another aerial port in your home (if you have one), to see if this makes a difference.