This warning without a log code is logged upon deployment of application:

13:06:16,312 WARNING [org.jgroups.conf.XmlConfigurator] (ServerService Thread Pool -- 101) version is missing in the configuration file

I can see this with several EAP Quickstarts, the exact list from CD20 is: batch-processing, bmt, cmt, greeter, hibernate, kitchensink, kitchensink-jsp, kitchensink-ml, managed-executor-service, spring-greeter, spring-kitchensink-basic, tasks-jsf, thread-racing

Not sure if it's relevant, but I have noticed all the above mentioned QS use H2. None of the QS that don't use H2 has the warning logged.

This can be reproduced with WildFly 20 Final release and WildFly 20 Final QS as well:
1. Start the server with $JBOSS_HOME/bin/standalone.sh
2. Deploy one of the above mentioned QS with mvn clean package wildfly:deploy

This warning was not present in CD19 and earlier releases.

The same warning was also logged on startup, which has been fixed with JBEAP-19734 and WFLY-13590.