Hi, I have a very similar issue. Spine 3.8.99 will open fine, but i need to run 3.6.53 for an old project. Spine runs, downloads old version, then nothing happens. But in the Finder launcher its running fine (hasn't crashed or hung). I checked the log and it says there's an "Error reading hotkeys.txt file" and error loading Spineboy project. I've reset and reinstalled everything and deleted the spine folder from Application Support as well but no joy.. I'm running an iMac 5k with default screen size.
Ah, I seemed to have found a fix (well at least for my setup). Before i was opening my existing Spine app (black and white logo) then manually setting the version i needed in the app settings, quitting and relaunching.
However, after I had 3.8.99 running again, I double clicked on a spine file and it opened the new Spine Launcher (red and black logo). I then changed the version in that dialogue from 3.8.99 to 3.6.53 and after launching, Spine switched to 3.6.53 and it's running fine. In fact both versions of Spine are running. Normally I open app from the launch bar at the bottom of the screen.
