It sounds like your WebFlux controller is not properly subscribing to the reactive stream, causing it to hang indefinitely. Given that the same service works fine when triggered from a Kafka listener or manually subscribed with subscribeOn(Schedulers.boundedElastic()).subscribe(), the issue is likely due to one of the following:

1. Missing subscribe() in the WebFlux Pipeline
2. WebClient or Redis Reactor Calls Running in a Non-Blocking Context
3. Reactor Context Loss in WebFlux
4. Incorrect Configuration of WebClient or RedisReactiveTemplate
5. Spring Context Not Managing the Reactor Execution Properly

Above are some guesses but I believe you might need to trace logs more and more to catch this issue. Good luck !