@Jack-van-Tilburg Same issue here (latest software versions): when selecting an item, the actions box pops up very briefly.
I've looked into the code a bit, stepping through it in the debugger, and I've noticed the pop-up becomes visible when, on line 473 of base.js, the CSS class "in" is added to the ".explorer-selectedactions" block. However, it immediately becomes invisible again as well, when stepping over this line. I can only assume a different part of the code reacts to the addition of the "in" class and changes the CSS to make the pop-up invisible, or perhaps the z-index isn't handled correctly by Apple. The "in" class is on the box when inspecting the element.
Just noticed it also popups very briefly when deselecting a previously selected row.
It only happens when selecting the first (or deselecting the last) item.