On my Demonhunter, which I dont play that often, I had the actionbars from elvui set-up previously.
Now with the actionbars from this addon, I dont see the bars filled. When I want to add a new spell to an "empty" actionbar, it wont "catch" it.

The issue was that somehow the other actionbars have been toggled off. (ESC > Interface > Game > Actionbars)

I enabled them and they are showing just fine.