I constantly have that message - my modem is right next to my landline phone because that’s where the only ethernet jack in my house is. It doesn’t bother me though. I’m getting new internet at the end of the month (up to 90mbps!) so I dunno what that will do. It’s only a message on my screen anyway.
The last 2-3 weeks I’ve been having problems with lag in multiplayer, to the point where it was basically unplayable. I quite often used to get “weak network connection” but it never affected gameplay until recently. Now it may just be a coincidence, but I had the same problem tonight, then did a cold reboot and went back into multiplayer and have had no issues so far.
I have also had a problem where it’s impossible to race online. It’s like you don’t ready up. I’m gonna try a hard reset though.