Probably the easiest way to check for conflicting IP addresses is to turn off the wireless on the router for a time, and to disconnect all the wired devices apart from the Mesh. Test the upload from the Mesh and if it is still wrong then my suggestion of possible IP conflict is wrong.
Alternatively but rather more complicated, you can check other connected devices from the HomeHub web page: Advanced Settings/Home Network/Devices on the HH3, probably similar on others. You then need to go through each device and check its IP. However, some routers only report its own DHCP devices and not devices connected with static IP.
Or you could check on the devices themselves; how to do that depends on the devices themselves so I can't tell you.
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It may be worth trying to plug the Mesh into a different port on the router. The single gigE port on the HH3 misbehaved for some devices, and there have been reports of other ports not working right as well. I don't know if the HH5 suffers similar problems.
It could be that the Mesh is trying to use GigE but can't really handle it. Try different explicit speed settings for it: probably won't help but worth a quick experiment. In Device Manager, Network Adaptors, right click on your adaptor name and choose Properties. Go to the Advanced tab and choose Speed and Duplex and play with the settings to see if anything helps. Note the initial value (probably Auto Negotiation) before you start so you can set it back where it was if the experiment doesn't help.
