Ubuntu 16.04 WiFi dropping on WPA group rekeying
Solution 1:
What fixed it for me was going to Edit Connections, choosing the particular connection, going to the IPV6 tab, and setting it to "Ignore".
That looks like IPV6 group rekeying.
Ubuntu has issues with their IPV6 on some systems. Mine worked great for 5 years. Then a after a routine update, it would drop consistently every 20 minutes. Disabled the IPV6, and back in business.