If it also occurs in the menu and also DCS, then a network issue appears unlikely in this case. But then again it’s computers so you’ll never know. Giving it a go without the additional router would be the first step I’d take and as DCS will also run offline, it should be a breeze to test that. Please report back with your results because others might find them helpful.
What Windows and NVidia driver versions are you running? Is it Win10 or 11?