Ethernet disconnect while playing Forza Horizon 4

I tested the game without bitdefender where it worked fine and after installing it again it Problem recurred.

my Problem is that after I click on continue in the intro menu my ethernet will always disconnect with the "message that my network cable is not connectet" or "no internet access". Sometimes it works again after 1 min or so and in most cases I have to restart my PC. I played the game already like 3 months ago where I had no such Problem only occured after reinstalling it 3 days ago. I also tried reinstalling the game which did not help. Video of the problem is also below.