@Koerthe Hi, thank you so much for the detailed network layout and issue description. Do you mean there is currently no issue with the "Current Setup" layout after you confirmed by ISP modem -> 8p...

@Dav3sky Hi, sorry to hear that. Can you pelase confirm if you have disabled the NAT boost on the C9? If not, give it a go and confirm, thanks.

@himanshu_c Hello, you can upgrade the firmware to the below one and confirm again: Archer C1200(US)_V2: https://static.tp-link.com/2020/202001/20200103/Archer C1200(US)_V2_180307(Beta).zip

@Neshcz Hi, thanks for updating with this valued info. Just out of curiosity, have you ever confirmed by connecting a computer directly to the ISP-provided modem/router at this periodical disconnect...

@japes Thank you very much for the details. There is no Speed negotiation settings on the green UI, can you please confirm where did you see this capped 100Mbps when connected to the C50? Do you...

@Paul_437821 Hello, thanks for asking. Can you please confirm what is the current hardware version and firmware version of your VR400? If it is V2, please try to downgrade to the previous Archer...