Trying to diagnose a drop in internet speed for computers not connected directly to my router.

[Solved] My office network has an internet connection which is approximately 80Mbps download. All computers connected directly to my router get approximately those speeds when I run a speed test. However, any computers which go through a hub to get to the internet will see a significant drop in speed to something like 20Mbps.

All of the computes are connected via Cat6 cable, and the router and hub are all gigabit connections.

The way I diagnosed this problem was by running a speed test on a computer connected to the hub as a benchmark. I then unplugged the cable from the router and the cable to the computer and connected them with a coupler (creating a direct link to the router). After doing this I ran another speed test on that computer and received nearly identical speeds to the other computers connected directly.

One question I have is whether it is normal to see speeds throttled like this after a hub, or if this indicates a problem with the equipment.

Due to the layout of the building it would be very difficult to have a direct connection of the router for all computers, so the use of hubs is necessary.