As discussed in the forum post, I couldn't reproduce the problem in another project even though I tried for days. So I trimmed down the original project to a similar configuration. I can't for my life see any real difference but the following fails to find producer in a jar.

Steps to reproduce:

1. git clone https://github.com/abhijitsarkar/java-ee.git
2. cd java-ee/hospital-appointment-system.
3. mvn clean install.