Hi found the answer here:

https://community.auth0.com/t/error-in-nextjs-15/151480

The answer was to upgrade again back to NextJs V15.0.3 following this:

https://www.npmjs.com/package/@auth0/nextjs-auth0/v/4.0.0-beta.0

it might sound silly that I downgraded to NextJs 14, but I have been using Auth0 with NextJs for a while using the dynamic API approach and when i downgraded, I compared the package.json with another working project. It seemed like a good idea to take that approach. After posting this and stepping back, i decided to try fixing the errors in NextJs v15 which has a different aproach to the dynamic API approach explained in the link above. Once I had that working, both of my issues were resolved.