It sounds more like a Netduma R3 configuration issue than a problem with your Virgin Media connection, especially since the router itself gets 470–500 Mbps.
I’d check QoS/Congestion Control, bandwidth limits, and any traffic prioritisation settings you changed for Black Ops 7. Try returning those settings to default and run another speed test. If the speed returns, you can adjust the gaming settings gradually without limiting the whole connection.
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