Same issue with circuitbreaker. The problem are the ReadOnlyHttpHeaders from netty.

java.lang.UnsupportedOperationException: null at org.springframework.http.ReadOnlyHttpHeaders.remove(ReadOnlyHttpHeaders.java:135)

https://docs.spring.io/spring-cloud-gateway/reference/spring-cloud-gateway/gatewayfilter-factories/removerequestheader-factory.html also not working.

<dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-gateway</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-circuitbreaker-reactor-resilience4j</artifactId>
        </dependency>

spring:
  cloud:
    gateway:
      routes:
        - id: test-route
          uri: id: test-route
          uri: http://httpbin.org/
          predicates:
            - Path=/test/**
          filters:
            - StripPrefix=1
            - name: CircuitBreaker
              args:
                name: exampleCircuitBreaker
                fallbackUri: forward:/fallback