This might be addressed later in the course, but just in case, make sure you untick the Cooldown Overlay image’s “Raycast Target” field otherwise it will interfere with your mouse click/drag and make it impossible to move items out of or between your Action Slots.
It’s actually not mentioned in the course. I’ll be sure to make a note to Sam to include this.
This solves my issue on a different part of my project.
spend couple hour to figure that out, trying to report, then found this post