I was puzzled by this recently and found it was due to slight mouse movement between the click and release. I can't remember the exact context but it was relate

I was puzzled by this recently and found it was due to slight mouse movement between the click and release. I can't remember the exact context but it was related to items that were drag-and-drop enabled. The press-to-select, move to drag, release-to-drop interaction was taking precedence over the press-release to click the button, even when the movement/drag was tiny, only a couple pixels. I can't think of an instance where I would dragging-and-dropping a button, maybe it was an anchor element or something else clickable, but perhaps it's an avenue to investigate.