Hub2 LAN speeds drop to 100MHz, resulting in perceived poor BB performance

[#1]

 I note that many reviews complain of poor speeds and I can suggest why. My router is connected to a 8m Cat6 cable to the main switch. When the router is new this works just fine, but the router rapidly develops a fault that the LAN connection drops back to 100Mbit from Gigabit and doesn't reset until you unplug the cable and force a renegotiation. If you are unaware of the problem this looks like low BB speed, but it's not it's just the LAN side of the router.
There are two solutions,
1. Buy a different BB router, but that's expensive and inconvenient.
2. Buy a £10 Gigabit switch and put that next to the router connected with a 0.5m cable. Connect your long cable to the switch. For me that stays at gigabit connection and I get my advertized speed, with a few occasional degrade periods of minutes as you get with any BB.

The first router I had did this, I had it swapped out and the replacement did the same within a month. It's a design fault with the router, it doesn't like long LAN cables. I tried replacing the cabling with a brand new Cat6 trailed across the floor, same fault.

If anyone can tell me how to stop this happening I will be grateful, but the fault is carefully diagnosed. To make certain I connected another machine to one of the other LAN ports on the router, and that only gave 100Mbit data transfer end to end showing that at least one LAN connection was 100Mbit. Also when I connected it by a 10m Cat6 cable after a few hours I could see on ethtool (linux) that the connection to this second machine on the router had dropped to 100Mbit.

I have 145Mbit fibre with a recent hub2 router

[#2]

@EmrysJ 

Ethernet plug contacts are basically IDC connectors with an incorporated contact strip. The sockets have a spring contact with some limited protrusion. I have made up some plugs that have failed to connect in some sockets. I put this down to me over-crimping the contact pins when fitting the plugs such that the socket strips had been pressed down below the reach of the socket spring contact. I believe that it only needs one of the control pins not making contact to turn the connection into a 100Mbps link

[#3]

@EmrysJ  The fact that this is only the second reply to your post suggests that the HUB2 does not have a design fault that drops the speed to 100Mbps or the forum would be flooded with users having the same problem. 

Speed issues with Ethernet are generally caused by the cables, such as the wrong type e.g. 2 pair when 4 pairs are needed for a Gigabit link, poor quality cable or faulty connectors as suggested by @Baldrick1 

[#4]

I’ve connected a 30-foot Ethernet cable to my Hub2, and it’s successfully achieving speeds exceeding 900 Mbps on it.