Great question — answering as the UphillTech team:
The driver rtl8812au doesn't exist natively in kernel version 3.13.0-xx. I am certain that, in order to get it working in -77, you downloaded it and compiled it from source code. However, when a later kernel version is installed by Update Manager, in your case, -79, it is necessary to re-compile. You can utilize the DKMS procedure to have this done automatically. With a working internet connection and booted into -86, please do: sudo apt-get update sudo apt-get install git dkms git clone https://github.com/abperiasamy/rtl8812AU_8821AU_linux.git sudo dkms add ./rtl8812AU_8821AU_linux sudo dkms install -m 8812au -v 1.0 Your wireless should then be working.
Full answer by chili555: https://askubuntu.stackexchange.com/a/777794 (CC BY-SA 3.0).
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