Theming App Not working after switching URLs

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Nextcloud version: 16.0.0
Operating system and version (eg, Ubuntu 17.04): CentOS 7
Apache or nginx version (eg, Apache 2.4.25): Latest nginx (using Docker)
PHP version (eg, 7.1): Latest PHP (Using Docker)

The issue you are facing:
After moving the domain that our Nextcloud server was at we are no longer able to use the theming app. If anything changes in the theming settings it is never changed in the running server, with the exception of the folder icons in the files view.

Is this the first time you’ve seen this error? (Y/N): NO

Steps to replicate it:

  1. Setup and use NC with theming
  2. Move the instance to an internal server using an internal DNS name
  3. Change theming settings and nothing sticks