After upgrade from JWS 5.5.1 to 5.6.1 the Kie server controller WebSockets stopped working, any WebSocket message ends with an error listed in attachment.

The issue can be reproduced only on Java 8. Java 11 works properly.

In community the issue can be reproduced on Tomcat by running:

mvn clean install -Ptomcat9 -Dit.test=WebSocketKieControllerManagementIntegrationTest -Dversion.tomcat=9.0.50

in kie-server-integ-tests-controller module.
Tomcat version 9.0.50 should match JWS 5.6.1.