I have been facing this problem in Ubuntu 16.04 LTS for over an year now and somehow there seems to be no fix online! Wifi appears to be hard blocked after the laptop wakes up from suspend. The only fix is restarting the laptop every time and that's annoying. I really want to quickly get back to my work and not restart my laptop every time. The wireless card is RTL8723BE.
On 16.04, I see this after suspend too. But I don't need to reboot. I can just reload the kernel module (driver):
sudo modprobe -rv r8723bs && sudo modprobe -v r8723bs
Not required to restart network-manager or nm-applet.
I use kernel 4.14.7 & 4.15.7 on a Lenovo ideapad 100S.
Newer kernels can be found in mainline ppa, eg: https://kernel.ubuntu.com/~kernel-ppa/mainline/v4.15.7/