RE: MBP Retina 13" Mid 2014 - Right side USB 3 port
Got an intermittent problem when plugging in either one of my external drives* to this particular port. Sometimes I lose my wifi connection. As soon as unplug from that port the wifi will immediately come back. This problem does not happen with the USB 3 port on the left side.
Do you think a SMC reset would be in order? Any thoughts would be appreciated.
TIA,
Alamedean
*Voyager S3 backup & Time Machine
Try the reset. Nothing to lose!
Q) Are you using the same cable each time? If so try swapping that out.
Q) Any chance these drives are directly between your Mac and your WiFi router when plugging in on the right each time you get a fail?
I had this problem when I connected a hard drive to my router. As soon as it was plugged in, the WiFi-range would drop by about 80%. We even got a replacement router but after that did‘t help, someone (maybe it was the company, maybe a search on the internet, I don‘t remember) told me that USB 3.0 cables can interfere with WiFi. Maybe there are cables that are better isolated? 
USB 3 can cause 8nterference with devices on the 2.4GHz band (WiFi, Bluetooth, baby monitors, etc.).
https://www.macobserver.com/tmo/article/usb-3.0-hard-drives-can-cause-wi-fi-interference
My external monitor blocks my WiFi signal (2.4GHz) from my AirPort Extreme. I bought a USB 3 to Ethernet and ran a flat cable, as I didn’t want to put my MacBook Pro on the other side of the monitor.
I had to buy a USB 2 hub and plug into my USB 3 hub for my mouse’s wireless adapter (the tiny plug receiver), as the mouse didn’t work well when it was plugged into the USB 3 hub.
So it’s very likely the connection to your external drive is interfering. You could try
- reorienting your laptop
- using a USB hub to plug the drives into
- getting a USB to Ethernet adapter and running a wire, if that is an option.
- Switching the network to 5GHz if that is an option