High CPU usage, framerate drop after adding or removing monitors

Hello,
On Ubuntu 14.04.5 LTS up to date (28/06/2018, DD/MM/YYYY), after connecting or removing a monitor (moving, etc...) with a Nvidia GPU, unity-control-center takes high CPU and makes Xorg taking 100% of the CPU.

This produces lags, framerate drop, etc... even with office apps (Firefox, LibreOffice, etc...).
It makes Steam and Discord very slow to start, and very laggy.
And Steam games run with 10 - 15fps were they run with 60fps or more without this bug.

Typing:
```killall -9 unity-control-center```

fix immediately the problem, but it's not good for users who don't know the reason and think it's due to a bad performance from Ubuntu....

Note: I use Ubuntu 14.04.5 LTS from about 4 years now, and I experience this bug only since 3 - 6months, on 5 different computers who are all up to date. (Kernel 4.4+, and all others updates)

Thank you !

PS: I don't know if it affects only computers with nvidia GPUs, but in my case I have the problem on all my computers...and they have all nvidia GPUs. Models used: GTX 770, GTX 1050, laptop and desktop, with and without hybrid graphics (intel).