Comment 1 for bug 1653307

Seems this is related to https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1380480.

I am affected as well by this bug like many other ubuntu 16.04 users.
There is several ways to fix this:

https://askubuntu.com/questions/766718/script-to-restart-network-manager-after-resume-from-sleep#766757

https://askubuntu.com/questions/761180/wifi-doesnt-work-after-suspend-after-16-04-upgrade

All are working fine, I finally opted for the last which seems more conventional with systemd, don't know though what's the best to use.
Anyway, basically the point is to restart networkmanager service.