Found the issue for anyone else with this popping up. There was a call to a custom Redux Extension that was not found. Make sure that in the options file or elsewhere in the theme, nothing custom is being called that’s causing a 404 error.
It’s a sandboxed dev machine with a the latest WP, Redux from the WP Repository, and nothing no other plugins. This is a clean install with just these two running and I’m getting those errors.
