I came across an issue related to the logic of io.opentelemetry.instrumentation.spring.webflux.client.WebClientTracingFilter class if spring reactive WebClient call is presented in the Reactor upstream chain.
Steps to reproduce:
For example - assume we have to call some external http service 1 but such a call should be preceded by another http service 2 call - in such a case last call resides in the upstream position with regarding to former one.
And parent open telemetry context for http service 1 will contain span under the following key - ContextKey.named("opentelemetry-traces-client-span-key") which is considered as a signal to not create new child span. But according to the logic of
io.opentelemetry.instrumentation.spring.webflux.client.WebClientTracingFilter.MonoWebClientTrace publisher - if mentioned above condition will be met - then subscribe method will be left without any subscription - and it is resulting in hanging subscriber chain.
I have found a work around to this problem by turning off spring-webflux-client instrumentation module - otel.instrumentation.spring.webflux.client.enabled=false - and then provides custom module which will be picked up by java Service Loader API.

public void subscribe(CoreSubscriber<? super ClientResponse> subscriber) {
  Context parentContext = Context.current();
  if (!tracer().shouldStartSpan(parentContext)) {
    return;
  }

  ClientRequest.Builder builder = ClientRequest.from(request);
  Context context = tracer().startSpan(parentContext, request, builder);
  try (Scope ignored = context.makeCurrent()) {
    this.next
        .exchange(builder.build())
        .doOnCancel(
            () -> {
              tracer().onCancel(context);
              tracer().end(context);
            })
        .subscribe(new TraceWebClientSubscriber(subscriber, context));
  }
}

But anyway it will be very useful to address such an issue. Thanks!