@Onknight While the AX20 is locked up, you can still check the IP address on the devices connected to it. Check this if there are computers. If the computer can get a valid IP address from the AX20,...

@My4GLTERouter Is your router model TL-MR6400 v4.0? How did you verify the 3G signal is weak, is there any detailed info? Who is the SIM card carrier? What if you put this SIM card into a phone, will...

@SSMP What if you roll back to the previous version, will the issue disappear?

@Ysbeer What is the speed you can get when you connect the same computer directly to the ISP modem? Can we have the speedtest screenshots? What is the cable length between the ISP modem and the C6,...

@Alexander24 Have you tried with a different computer or device? What is the Ethernet adapter on it?

@Pepsi96 Is your router Archer C6? It is suggested to upgrade the beta firmware and disable Onemesh on it, then monitor the stability: https://community.tp-link.com/en/home/forum/topic/207232