USB-C dongles killing Wi-Fi on 2016/2017 MacBooks – Who’s to blame?
One customer got a good USB-C Hub and after plugged it to their MacBook Pro then appears the same wifi interference problem.
He solved the interference by covering the Hub with aluminum paper
(Thanks Faraday!)
Blame physics. The inverse square power law means that a signal that is very weak a few feet away can cause severe interference right next to the Bluetooth and WiFi disrupting the 2.4 GHz signal.
Now, if the Mac works without any accessories, you have to blame the accessory or purchaser of the accessory of you insist on a blame centric worldview. For most people, understanding that interference can happen helps them find practical remedies.
So now the blame shifts engineers for working on products they know can’t be reliable and doing what management asks. Some engineer somewhere designed the hardware and blame government for not checking the engineer was licensed or clawing back licenses when people ship garbage hardware. Least to blame is companies that don’t support good hardware that can have failures.
Great shielding can help as can drivers that literally turn off the USB 3.0 signal periodically to give the WiFi a better (slim) chance to get some traffic through.
- https://www.intel.com/content/www/us/en/io/universal-serial-bus/usb3-frequency-interference-paper.html
- https://www.pcmag.com/article2/0,2817,2423604,00.asp
- http://support.logitech.com/en_gb/article/38032
Unless you can somehow separate the devices physically, even with ideal 2.4 GHz radio conditions of low noise and good signal, with properly designed, properly assembled and correctly operating USB 3.x hardware, they can interfere significantly with the older WiFi standard channels in the 2.4 GHz range.
If you use a lot of the newer adapters, you'll want to be sure you have a good 5 GHz wireless network running. You'll also need a way to measure / triage / eliminate faulty or poorly designed USB 3 devices - they will ruin many people's day with interference.
The good news is the power of the good devices is low and the inverse power law prevents a USB 3.0 device from interfering with 2.4 GHz signal across the room, but for the computer connected, they are simply too close in most cases to rely on both 2.4 GHz WiFi and USB 3 together.
Foil Wrap works!!! No more slow wifi and dropping network connection after wrapping 2 hdmi multiport dongles.
Got my Ugreen type-c adapter works with extension cable! External hdmi display, usb 3.0 hdd and mouse are works fine! No problem with wi-fi or bluetooth. 
I was having this same issue but was able to come up with a work around. By using google speed test and having one cable plugged in at a time, I was able to determine that my front right USB port was the problem. If I have it plugged into my usb hub or monitor from that port, my wifi takes a turn for the worse. (Note: the wifi source is located on the right of the computer, so maybe it would be the left side if your wifi source is located on the left of the computer.)
Luckily, I noticed the issue does not persist if the power cable usb-c is plugged into that port. So, I just have my ports arranged so that my power usb-c is always plugged into the front right port.
For testing it, go to google speed test. And as the test is running, place and remove your hand over your ports. For me, I could clearly see that change of speed if my hand covered the ports. Find a cable that causes a problem, and then test each port individually. Hopefully, the problem is not as bad in some of the ports. If so, then use the ports where it works well, and for the bad port or ports, use it for the usb-c power cable only. Good luck!