Internal error 500 accessing Theme > Customize

Question

We have created a basic custom theme for WordPress. When trying to access Appearance > Customize from the backend we receive an internal error 500. I have checked the error logs and cannot find anything relating to this.

The website is working fine, the theme is working fine as expected, just accessing the customize section.

Do we need to include anything specific in the functions theme file to be allowed to access this section? Does a part of the theme have to be customizable in some way? I have tried various searches for this, although the basic 500 errors seem to come up a lot. I.e. htaccess, plugin issues.

Answer 1

Just in case anyone else finds this in the future. The issue was that we had an error/warning in our functions file.

When accessing widgets we noticed the error/warning from the file. Resolved this, then the customizer link provided us with an on page error.

The on page error linked to a reimplementation of a method from within a plugin. The plugin was overriding a core method so we removed it and now works as expected.