MacOS 10.15.7, Unity 2019 LTS, Playmaker 1.9.1 (with the all new shiny UI).
With the 1.9.0 I already noticed that it was getting difficult to strike a tick in the box and sometimes I had to click twice or thrice but now it's almost impossible if the window isn't docked as a tab somewhere, it's hijacked by the higher Unity UI's double-headed arrow ⤢.