This issue is minimally reproducible by using the latest API Platform distribution template. You will need to run the production Docker config to use FrankenPHP in worker mode.

Add the Lexik JWT authentication bundle to a new project and configure an auth endpoint as per normal.

Add an API resource with some validation constraint on it.

Use the following configuration for packages/api_platform.yaml:

api_platform:
    formats:
        json: ['application/json']
        jsonld: ['application/ld+json']
        multipart: ['multipart/form-data']
    defaults:
        formats:
            json: ['application/json']
            jsonld: ['application/ld+json']
            multipart: ['multipart/form-data']
        extra_properties:
            rfc_7807_compliant_errors: true

Make a request to your auth endpoint and obtain a token, authenticate with this token against a request to your API resource to a POST endpoint, but in the request body, violate your validation constraint to return a 422 response.

Now immediately call your auth endpoint - you will get a 404 error, because Symfony will determine the authenticator doesn't support the request - and because the auth endpoint doesn't have a real controller, when the authenticator doesn't run, no controller will be resolved and the route won't be matched to anything. This is happening because in the long-running worker, the 422 response has returned application/problem+json and overwritten the request format mimetype mappings (which are static) in the HttpFoundation Request class probably by calling setFormat somewhere.

The fix is to use the corrected config like below:

api_platform:
    formats:
        json: ['application/json', 'application/problem+json']
        jsonproblem: [ 'application/json', 'application/problem+json' ]
        jsonld: ['application/ld+json']
        multipart: ['multipart/form-data']
    defaults:
        formats:
            json: ['application/json', 'application/problem+json']
            jsonproblem: [ 'application/json', 'application/problem+json' ]
            jsonld: ['application/ld+json']
            multipart: ['multipart/form-data']
        extra_properties:
            rfc_7807_compliant_errors: true

But the documentation for API Platform on content negotiation and error handling really isn't clear. This caused a bug for me in a production environment that took ages to track down and gave me a headache, so for the benefit of others in future, please address this somewhere. Thanks.