I suggest using the latest version of Spine if you can. 3.5.51 is very old and the crash you see is caused by running a newer version of Spine, then going back to 3.5.51. To use 3.5.51 you will need to reset your settings by deleting this file:
Windows: <user home folder>\Spine\prefs.json
Mac: <user home folder>/Library/Application Support/Spine/prefs.json
Linux: <user home folder>/.spine/prefs.json