Branding API: GraphiQL app Access denied on development store with extensibility preview enabled

Hi,
Similar question has been asked before but does not solve my issue. I have been using the Shopify GraphiQL app in order to query/mutate the Admin successfully for months now. Yesterday after one of many successful queries I started getting the same error message, even though the code/query is all the same:

“message”: “Access denied for checkoutBrandingUpsert field. Required access: The app must have access to checkout branding settings and the shop must be on a Plus plan or a Development store plan.”,

I am already on a dev store with extensibility enabled and have never had this problem in the past. I created a new dev store again with extensibility enabled and still the same error happens. I contacted Shopify support and received a basic response telling me I need to be on extensibility preview but I already had that enabled.

I also gave the GraphiQL app ALL permissions for Admin & storefront so none of this is making sense.
Please help, I am on a client project.

Switching to my laptop to reinstall GraphiQL app fixed this, although re-installing on my desktop was showing the same error.