Unfortunately those two versions are not supported:
Our supported technologies page states that spring-webflux is supported for spring version 5.2.3 or newer. Spring 5.2.3 ships reactor-core in version 3.3.2.RELEASE, which is the earliest supported version.
When I exclude this class with argument
-Delastic.apm.classes_excluded_from_instrumentation=reactor.core.*I see no error. Can I use this arg without problems?
I would recommend you to rather disable the problematic instrumentation than relying on the package names. You can do this using the following option:
-Delastic.apm.disable_instrumentations=reactor,spring-webflux,springwebclient