We're missing reflection hints for some of the types that are returned by loggers. They aren't picked up automatically via @Endpoint being @Reflective because they're hidden behind the method's Map<String, Object> return type.
Comment From: wilkinsona
We should be able to fix this using @RegisterReflectionForBinding({ GroupLoggerLevels.class, SingleLoggerLevels.class }). It doesn't work at the moment as there's a clash with the @Reflective meta-annotation of @Endpoint which causes @RegisterReflectionForBinding's processor to be ignored. I've opened https://github.com/spring-projects/spring-framework/issues/29193.
Comment From: wilkinsona
We wouldn't need all of the hints that @RegisterReflectionForBinding would give us so https://github.com/spring-projects/spring-framework/issues/29194 could be relevant here as well.