Spring Boot Websockets in Wildfly

You need exclude tomcat-embed-websocket

<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <exclusions>
            <exclusion>
                <groupId>org.apache.tomcat.embed</groupId>
                <artifactId>tomcat-embed-websocket</artifactId>
            </exclusion>
        </exclusions>
    </dependency>