Google Index Coverage - Error 5xx

The new Google Index Coverage has notified me of an error 5xx, with the following:
http://queenketo.com/?customize_changeset_uuid=06975c76-2c11-419c-9b10-7c4deab699b4&customize_theme=sydney&customize_messenger_channel=preview-19
I no longer have Sydney installed (due to other issues I couldn’t address), and cache was cleared. What does the above mean and how can I fix it, please?

Hello,

It doesn’t seem to be a theme issue. You might want to check these links:
https://productforums.google.com/forum/#!topic/webmasters/2ZuQFFbLVxM

Kind Regards, Roman.

Hi Roman, the error is a 5xx, not 404. Also, “theme=sydney” is showing in the url that appears to be the problem. Could there be a piece of code left behind that’s causing an issue? P.S. I have no technical ability or help from anyone.

Hello,

It looks like this issue requires close inspection, this goes beyond our support policy. As an option, you can contact Codeable for this kind of service, or find a reputable freelancer on Upwork.

Kind Regards, Roman.