Internet speed drops to 2-3Mbps after switching between ISP's via Ethernet

Hi. I have a very frustrating issue. I have 2 internet connections in my home through different ISP's. One is cable and the other is through the phone line or some form of that technology. One has higher upload speed and the other higher download speed which is why I have both. I use the higher upload speed for work and the other for every day things. I connect both via Ethernet. Simply unplugging one to plug in the other and vice versa.

The higher download speed one(Virgin media) has 220Mbps download speed. The Upload one(Sky Broadband) has 45-50Mbps download speed. The issue is occasionally when I switch between them the speed drops to 2-3Mbps on both permanently but only on this PC and only the dopwnload speed is affected. The upload remains normal. This does not happen every time but when it does happen it is stuck that way. No matter how many times I try to reconnect them or restart the router/PC it is this speed. Also when this happens I have a lot of connection issues where somethings give errors and refuse to load.

things I have tried:

Diagnostics in windows 10 on the adaptor.
Disable/Enable adaptor.
Manually changing duplex settings to 100 then back 1Gbps then back to auto. This actually worked in a sense. I was able to get 100Mbps download but then switching it back to auto or 1Gbps dropped it back down to 2Mbps. The connection speed shows as 1Gbps and every diagnostic I run from router or on pc shows it to be that speed and working ok.
Some DNS flush thing in CMD I found online.
Reinstall Lan Drivers.
Various combinations of restarting router unplugging Ethernet and restarting PC.
Perhaps some more things but I cannot remember off the top of my head.

Interestingly the only thing that fixes the issue is a system restore. The reason it is interesting is that I can create a restore point whilst the issue exists then restore to that point and the issue is gone.

I am at my wits end trying to fix this so any suggestions I am happy to give it a shot
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  1. Best answer
    Try another method to eliminate that it is a hardware issue. Let your router that you use the most run normally. On the other router change its IP to something like the main router is using Now disable the DHCP on the second router and run a cable between the lan ports.

    Now to switch back and forth use the ROUTE command. Issue a ROUTE DELETE mask and then ROUTE ADD mask

    Now if you really want to get ambitious you can use the route add command to add routes to the second router just for particular IP addresses and use both connections at the same time. It tends to be tricky to setup if you have more than just a couple of ip addresses to run to the second connection.
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