Failed to load resource: the server responded with a status of 500 (Internal Ser

I am in the process of migrating a WordPress site to Amazons Lightsail service but have run into a problem with certain files used by a theme called Elision (very old theme now). I was hoping to get any suggestions as to how to solve this or perhaps any additional ways to try and debug the problem. I have provided the link to the site.
Other css/js files on the site seem to be fine, but anything related to the Elision theme/Qode it gives 500 error.

Things I have tried:

• Regenerating the .htaccess file
• Deactivating all plugins
• Swapping themes
• Double checking file permissions are correct

The page I need help with: [log in to see the link]