Live TV channels are delivered over your "broadcast" TV signal, whereas your apps such as iPlayer, Netflix, Amazon & VOD are delivered over your internet connection.
It therefore sounds like you may have a fault with your incoming TV signal. I'd recommend one box reboot to eliminate gremlins, if the problem continues then it needs reporting to VM who should either arrange an engineer visit or box replacement.
Are there any particular channels affected, this may help narrow the fault down?
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