I am a newbie but have both the Phantom 4 and a Mavic. Been flying the 4 for a couple days and never got this message flying from the exact same spot. Mavic flew fine (except for my impatience and forgetting to take protective film off forward sensor causing it to sense objects not there) but I did get this message. What is going on and how serious is it?

I get this message popping up occasionally but if it goes away I don't worry about it. I fly in the city so there are a lot of wireless  networks. If the message wouldn't go away I would RTH.

Do Powerline cause similar issues too? Just wondering.

I have also experienced the message in the middle of no where. #2 advice is recommended.

Same here never got message. Now wont go away

I ignore this message as i see several bars of signal strength

I've had the message as well.  I pay closer attention to the drone if I am using intelligent flight modes but I haven't had any "controllability" issues.  I believe the connection between the drone and the controller is pretty robust with regard to interference, but they obviously have the warning for a reason.

I’ve received this message as well and what I’ve found it’s refers to the WiFi on the device being used. iPad mini 2 WiFi version, when flying at home if I don’t turn on airplane mode I get the warning, but never when am away for WiFi.