I'm using Zen as my browser, but I'm having the same issue with Google Chrome. I have deleted data, cookies etc. and the issue persists.

On my account it says I am an Active Guild member, with a Grandmaster tier subscription. However I'm trying to change the Styling for my world and it says I need to be a member to do that.
It brings up the Guild Subscription popup box, with the small option at the bottom that says "If you're already a Guild Member 'click here' to fix. I click it, the page reloads, but the issue is the same.

I am logged into my account.

I go to my Panriel world.

I click 'Go To Advanced Settings'

and it comes up with the small box saying "Join the Worldbuilders Guild!" even though I'm already a member.