Hub 5x faulty Ethernet port

I’ve just had Virgin Media installed. I’m in a nexfibre area and am getting the full 1.1 Gbps up/down to the Hub. I have a 2.5 Gb network card and am using the 10 Gb port on the Hub 5x. However I believe the 10 Gb port is faulty as it returns very sporadic speed results, especially on the downstream. What I have done to isolate the issue:

• Restarted/reset the Hub 5x
• Light is solid white
• SamKnows RealSpeed confirms the Hub is receiving the full speed 
• Tested different Ethernet cables with different devices on both the 10 Gb and 1 Gb ports
• Manually configuring the speed and duplex on each device to ensure auto negotiation isn’t causing the problem

What I have found:

• The 1 Gb ports consistently return 940/940 on speed tests, on all devices and cables I’ve tested
• The 10 Gb port has sporadic results from 300-800 Mbps on the downstream regardless of whether the device is 2.5 Gb or 1 Gb enabled

So, the 2.5 Gb device gets higher downstream results (and more consistent) using the 1 Gb port on the Hub, which is obviously not right. The 1 Gb devices get slower and inconsistent downstream speeds when switching from the 1 Gb to 10 Gb ports. 

Note the engineer also had issues activating the Hub when it was installed (it eventually came online the next day). 

I have also had an issue as my Virgin Media account and the app still say my services haven’t been installed yet (which they have for a few days now). 

I’m really hoping I can just get a replacement Hub as it’s clear something is up with the 10 Gb Ethernet port, and also this issue with my account resolved.