Basically, due to this piece of code:

The last created warning decides wether all the created warnings are limited or unlimited. Thus in fastify, since last created warning is made unlimited:
https://github.com/fastify/fastify/blob/99a405a4e347629595ac5062c74d91675b1b34e5/lib/warnings.js#L58

warning.create('FastifyWarning', 'FSTWRN002', 'The %s plugin being registered mixes async and callback styles, which will result in an error in `fastify@5`', { unlimited: true })

All the declared warnings are spamming the application :)

Should either move opts inside "create" or add a new hashmap for the unlimited flag