The real issue is here in this comment : spring-cloud/spring-cloud-kubernetes#1677 (comment)

I will try to simplify this as much as possible in order for you to re-produce it. Simply clone this repository : https://github.com/wind57/spring-maven-sources-plugin-issue/tree/main

and issue a mvn clean install. It will fail with a :

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-source-plugin:3.3.1:jar (attach-sources) on project demo: Presumably you have configured maven-source-plugin to execute twice in your build. You have to configure a classifier for at least one of them. -> [Help 1]

The cause of this issue is in that comment in the spring-cloud-kubernetes project. If there is anything else required from me, will be more then glad to provide. Thank you