It shouldn’t be the panel’s properties.
My ACM mod uses 4 different UI’s, and all of the panels - and all background elements/images/effects - are all set to Self Hit Test Invisible.
I believe I had this issue early in my UI days and part of the problem I had was in fact visibility, but it was the individual widgets/elements that were the issue, they default to the above which won’t register mouse clicks.
-WM