Great diagnostics so far! Most of those channels share 3 common broadcast frequencies, this is strong evidence of a problem with your incoming digital signal, or possibly a box tuner fault.
The resolution is the same, I recommend you call Virgin TV Faults (150 from a VM landline, otherwise 0345 4541111) and report this. Depending on what their remote diagnostics suggest, you may need a replacement box to be sent out, or an engineer visit to be booked.
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