I gave another go, I cliked all the spheres on the last try, single click, double click, click and drag, finding the center to click... I tried on browser window and full screen and still the sphere wasn't clicking.
Maybe the window resizing causes the collision shape to relocate from UI grid? I full screened it at the other resolution before it was changed but I didn't test on the resolution it was at originally...
Edit:
Maybe it's an Itch mouse issue, as on this zommed in screenshot, what seems to be the center of the light is atop the sphere but visually, my mouse is approx. where I've circled. My game also has mouse issues...
I've also clicked around using the center of light instead of my mouse and still couldn't do anything :\
