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The obvious thing to check is that all leads are securely fixed.
If you still have problems, you may want to rule out a fault on your own kit. What happens if you swap cables around connecting directly between the TV and V+ without the amp? Does the fault occur if you use a scart instead of HDMI?
If the fault persists you'll need to call VM faults, the difficulty for you is ensuing its the VM kit and not your own that has gone wonky.