Network problem: proxy settings could not be determined automatically?

Following problem:

I get the error message every 10 to 30 minutes:

Proxy settings could not be determined automatically.

The internet connection is lost. After 1-3 minutes I have internet again.

I'm pretty annoyed by it now and would like to fix the problem.

Hardware:

Fritzbox

https://www.amazon.de/...07GX5SWV3/

TP Link Powerline Adapter

https://www.amazon.de/...00C2ICYPC/

I connected the powerline adapter to the laptop (Windoof 10) via LAN.

Is it perhaps because the "power network" over which the DSL signal is distributed is diffuse and therefore the proxy can sometimes not be determined?

Theoretically, the laptop should also have WLAN available (connected) and if no network can be determined via LAN, switch to WLAN.

Under Windoof 10 settings there's a tick in "Obtain proxy automatically". So it can't be because of that.

Can someone help?

Possible causes?

Check which settings'?

Is it because of the Fritzbox or the provider?

No, it's not the provider's fault, it's a local problem
Sounds like Powerline and WLAN are "connected" to your laptop at the same time. Of course, that can't work. Please choose a connection.
The internet connection in your Fritzbox may be set so that the DSL connection is disconnected when not in use. Then please switch the internet connection in the Fritzbox to permanently on.
The proxy connection settings are correct by default. There's no mistake. The problem is the unstable LAN / WLAN connection.
There are other possible causes, but rather unlikely…

Thanks for the fast respond.

I didn't check the "Connect WLAN automatically" option. I.e. I'm primarily connected via LAN. So no simultaneous use. When the error message comes up, I tried to connect to Wi-Fi to see if it was due to the powerline adapters. If that were the case, the (normal) WLAN that the Fritzbox sends out should have a connection possible. But it doesn't work. Error remains.

I don't think I've set "Automatic disconnection when not in use", I don't have a data plan or something. In addition, the error usually comes when I'm online. The browser shows "Page could not be loaded". So it can't be.