The magic happened again (struggle for two days, ask the question, find the answer an hour later)
The .jar files produced take the name of the directories at the end of the path, so they have to be different in every module, otherwise the first generated one wil be replaced by the second. Instead of
lib/dummy/common
lib/dummy/jvm
lib/utils/common
lib/utils/jvm
I have
lib/dummy/dummy-common
lib/dummy/dummy-jvm
lib/utils/utils-common
lib/utils/utils-jvm