smallrye-reactive-messaging: RabbitMQ - BackPressureFailure: Buffer full

I am regulary getting BackPressureFailures from my RabbitMQ consumer in my Quarkus (2.12.2-Final, Java 17) application.

io.smallrye.mutiny.subscription.BackPressureFailure: Buffer full, cannot emit item
	at io.smallrye.mutiny.operators.multi.MultiFlatMapOp$FlatMapMainSubscriber.failOverflow(MultiFlatMapOp.java:541)
	at io.smallrye.mutiny.operators.multi.MultiFlatMapOp$FlatMapMainSubscriber.tryEmit(MultiFlatMapOp.java:243)
	at io.smallrye.mutiny.operators.multi.MultiFlatMapOp$FlatMapInner.onItem(MultiFlatMapOp.java:607)
	at io.smallrye.mutiny.operators.multi.MultiMapOp$MapProcessor.onItem(MultiMapOp.java:50)
	at io.smallrye.mutiny.operators.multi.MultiMapOp$MapProcessor.onItem(MultiMapOp.java:50)
	at io.smallrye.mutiny.subscription.MultiSubscriber.onNext(MultiSubscriber.java:61)
	at io.smallrye.mutiny.vertx.MultiReadStream.lambda$subscribe$2(MultiReadStream.java:77)
	at io.vertx.rabbitmq.impl.RabbitMQConsumerImpl.lambda$handler$0(RabbitMQConsumerImpl.java:59)
	at io.vertx.core.streams.impl.InboundBuffer.handleEvent(InboundBuffer.java:239)
	at io.vertx.core.streams.impl.InboundBuffer.write(InboundBuffer.java:129)
	at io.vertx.rabbitmq.impl.RabbitMQConsumerImpl.handleMessage(RabbitMQConsumerImpl.java:150)
	at io.vertx.rabbitmq.impl.QueueConsumerHandler.lambda$handleDelivery$0(QueueConsumerHandler.java:39)
	at io.vertx.core.impl.ContextInternal.dispatch(ContextInternal.java:264)
	at io.vertx.core.impl.ContextInternal.dispatch(ContextInternal.java:246)
	at io.vertx.core.impl.EventLoopContext.lambda$runOnContext$0(EventLoopContext.java:43)
	at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:174)
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:167)
	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:470)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:503)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.lang.Thread.run(Thread.java:833)
	at com.oracle.svm.core.thread.JavaThreads.threadStartRoutine(JavaThreads.java:596)
	at com.oracle.svm.core.posix.thread.PosixJavaThreads.pthreadStartRoutine(PosixJavaThreads.java:192)

The weird thing is that I have configured max-outstanding-messages, so in my understanding it should be impossible to get this error.

mp:
  messaging:
    incoming:
      new-message:
        automatic-recovery-enabled: true
        max-outstanding-messages: 2
        exchange:
          name: x
          type: topic
        queue:
          name: x
        routing-keys:
          - x.#

Here’s the code that handles messages. consume contains a catch-all statement.

   @Incoming("new-event")
    @Blocking
    public CompletionStage<Void> newMessage(Message<?> message) {
        var meta = message.getMetadata(IncomingRabbitMQMetadata.class);
        meta.ifPresent(amqp -> {
            var key = amqp.getRoutingKey();
            LOG.info("Message {} received", key);
            consume(key, amqp.getHeaders());
        });
        return message.ack();
    }

Any ideas how to approach this?