What's wrong with the internet on my PC?

I have a question A few months ago I had a new PC built for me. Since he has been here, something is wrong with the internet connection. (It wasn't like that on my old PC). Normally, as a comparison, I have a download speed of around 17 Mbit per second in the DSL speed test. But when I start up my new PC I only have about 1 Mbit per second, which is mega slow for downloads. I have a house and a LAN cable is not directly connected to the router but connected via 2 adapters. One next to the router and one in my room. But if after booting I plug the adapter out and back in next to the router everything works as it should, only that's bad if I do it every time because something else can break. In addition, the internet speed drops again after a while and I have to plug the adapter out and in again. This was not the case with other devices like my Ps4 or my old PC. Does anyone know why?

Except that you install the original motherboard chip set and LAN / WLAN drivers from the manufacturer and, if necessary, check the adapter with another PC, remote diagnostics are hardly possible.