Hi I hope my experience will help you. I work in the field for virgin media and have seen this problem before. I have resolved it by changing the Eside in the mux. You'll need an engineer to do this,I dont think you'll get through on the phones but if you download the virigin connect app you'll be able to book a visit there.
I am a serving Field Technician at Virgin however all responses on here are based on my experiences in the field alone and my own equipment at home and should be taken as such
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