MacBookPro (Sierra) brings down WiFi network

[zocarius]

Our devices
We have a household with two MacBook Pro's (one Sierra, one El Capitan), and iPhone 7 and an Android Nexus 6.

The problem
Yesterday, seemingly out of the blue, the WiFi stopped working for my wife. When we investigated, it turned out that every time she connects her MacBook Pro to the WiFi router, the WiFi connection drops for all devices. Resetting the WiFi router resolves the problem and if her MacBook Pro is not on the network, all other devices work flawlessly. If her MacBook Pro connects, WiFi works briefly (20 seconds or so), even on her MacBook Pro, but then breaks again.

A strange symptom
One other strange and possibly related thing: we've noticed is that System Preferences is now often hanging on her MacBook Pro when WiFi is on. Not having seen System Preferences hang in 10 years of Macbook use, I thought this was a little suspicious.

Tried so far
I've tried to find help online, but most articles deal with WiFi issues dealing with one device. I've following this page's instructions (minus resetting SMC or PRAM) to no avail.


Does anyone know possible causes for a MacBook Pro bringing down the WiFi network for all other connected devices? Thank you!

 

[keysofanxiety]

You can try to change the wireless encryption on the router to WPA2-PSK (also called WPA2-AES) only; no mixed/legacy mode.

It's definitely worth resetting the PRAM/SMC on the Mac. Failing that, you can try to create a nwe user account to see if it works through there. This will at least diagnose if the problem is software related. Let me know how you get on.

 

[Taz Mangus]

Create a new user account, reboot the computer and try using the WiFi from the new user account.

 

[zocarius]

Thank you for your answers!
The router was already set to WPA2-AES, @keysofanxiety.
My wife reinstalled Sierra and at first it worked, then it cut out again, but after another router reset it has been working for the rest of the night. We'll see how it goes, but if it plays up again, I will try your suggestion, @Taz Mangus.

 

[zocarius]

It cut out again in the morning (consistently) and switching user accounts unfortunately did not help. Using an ethernet cable (and converter from ethernet to thunderbolt) seems to work fine, so it seems to be something about the WiFi connection between the specific Macbook Pro and the router that is causing problems, breaking the connection for all.
Hmmmm....