@MultiRouter Check that your cables support Gigabit (Cat. 5e or Cat. 6), that they are well built (ideally use a tester) and that your connected devices have Gigabit ports.

As you can see in the screenshot from my main router (archer ac2300), the internet speed from my main router (archer ac2300) to my second router (the archer c6) is limited to 100 Mbps. The second router is in access point mode and connected via a cat5e cable so 1000 Mbps should be the case. Has someone found a solution to this?

@internet123 Hello, I have the same issue, directly to the ethernet cable I can see my 200MB but my router limit it to 100MB, my status is the same as yours.

Do you found any solution?

@HumarMorenoB 

Follow this thread to troubleshoot your issue - [Troubleshooting] Speed limit to 100 Mbps