Hey ric1 --
1) If you post your open api spec happy to help you debug in more detail.(I have heard the Native Generator: https://openapi-generator.tech/docs/generators/java works the best)
2) My team has been working on a Swagger alternative that really focuses on codegen (as Swagger was initially built for docs) and we are calling it Fern. Repo here. Demo video here.
It is as easy as
npm install -g fern-api (to install)
fern init # initializes a basic fern api
fern add java # adds java generator
fern generate
