Network speed difference between Hyper-V host and VM

My Windows Server HyperV host can achieve SpeedTest.net results of around 60Mbps down / 10Mbps up.

I have a Ubuntu 18.04 VM running on this host and that achieves 58Mbps down, but only 3Mbps up.

I have another VM, running Windows 10, which achieves similar results to the host - 60Mbps down / 10Mbps up.

Any ideas what could be slowing down the Ubuntu VM?

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