Irregular signal disturbance on TV since the internet became available

TV software?
The device is probably also connected to the LAN because of [Smart TV]? When you turn it on, it must quickly recognize which signal it should output. That may not always work immediately? Just a guess

I noticed that the error mostly occurs within the first minute when I turn on the TV and the signal then disappears for about 20 to 25 seconds.

It sounds like some device in the TV chain needs to reboot and therefore sends nothing for 20 seconds. Can you see if any devices are restarting? Do they have LEDs that could indicate this? I didn’t quite understand your setup completely. Which devices are connected between the satellite dish and the TV? Are there cross-connections to the router? I would unplug all cables from the satellite devices that are not necessary, meaning any LAN connections.

Do you have Telekom Sat Entertain?

Hello everyone. So at first, I removed the internet connection from the router. That did not improve anything. A day later, I disconnected the power cable from the router but left the internet connection attached. That initially also did not improve anything. However, since Friday, it has not occurred anymore. I am waiting to see. The multiswitch is located in our attic. No one has been there.

No, we do not have Telekom Sat Entertain. Between the satellite dish and the TV, we only have a multiswitch, and I have installed a spawn so that we can record on our TV device and watch simultaneously. However, that has been installed since we moved in and did not cause any problems until the internet connection.

If the problem occurs again, I will disconnect the LAN connection from the TV once more. However, the internet came into the house about 6 weeks ago. I made the LAN connection to the TV one to two weeks later. If I remember correctly, the connection has been disrupted since the day of the internet connection.