Katlin,
I do not know where the error lies. If AC 20 v.3016 was installed on OSX Yosemite, pop up window of the license confirmation is showing each time when the program was started.
When installing 3016 on macOS Sierra such a window did not pop me, but pop up after installing each subsequent update.
So AC20 v.3016 no pop up of EULA confirmation's window, 4012-window pops up, 4020-pops up, 5025 window pops up, 6005 window pops up.
The problem also occurs in AC 21, I'm run the program, pops up the confirmation window of the license terms, I'm click Accept button, continuing the program startup.