kxs Spine v3.8.79 How to reproduce: Open spineboy-pro project and clone the skeleton. Select multiple slots in first skeleton and second one using Ctrl button. Change visibility of any of selected slots trying to do this for different slots.
Nate Good find, thanks! We'll fix this in 3.9. Note it actually does toggle the slots, the tree just does not update correctly. If you change the tree filters so the tree updates, you'll see the real state of the slot visibility.