I have the same thing happening with a Maxtor usb stick. When I plug it into my 2017 MBP (via a usb-c to usb-a dongle), wifi connectivity will drop to what feel

I have the same thing happening with a Maxtor usb stick. When I plug it into my 2017 MBP (via a usb-c to usb-a dongle), wifi connectivity will drop to what feels like an unreliable 1200 baud connection. Apparently, it is an issue due to the metal unibody. It took me way longer than I care to admit to figure out the usb stick was causing the problem. :-( Fun fact: try gently swiping your finger over the unibody while charging, and then without charging. You'll feel something like a vibration in the former case. I prefer quality plastic.