It could be both a bug and a once in a lifetime error. 😉 If Spine crashes, it's definitely a bug and we'd love to fix it. The error shows the mouse went down on a list, but not much else. You are running 3.6.50 which is very old (1 year and 5 months old! :scared🙂. There have been many bugs fixed since then, some of which are related to the Weights view (which has a list). Maybe you were clicking the bone list in the Weights view? You might consider updating to 3.7. There are not super big differences in the runtimes between 3.6 and 3.7 so it should be pretty smooth (but as always, be sure to test thorough before saving your projects with 3.7!). At the very least you should update to 3.6.53, which is the latest 3.6 version. It is very safe to update from 3.6.50 to 3.6.53.
