So it looks like they fixed it in R80.30, as I cannot reproduce the issue I faced in R80.20.
There is also protection that will not install the policy via Scheduled policy installation on the gateway which wasn't installed before. For example, my original policy package name for gateway GWC is POLICY_GWC.
If I select that I want to install Standard policy on all gateways (including GWC), the Scheduled policy installation did nothing for GWC gateway. It will not install Standard policy package on gateway GWC (where is expected to be policy package POLICY_GWC).
Kind regards,
Jozko Mrkvicka