Be sure that you compile your project on a given OS/architecture and with a given compiler version. Also ensure that all your dependencies have an imposed version (use maven-enforcer-plugin for that).
If you find other interesting sources of "non reproducible" data that this plugin could remove, please open a ticket in the bug tracker or send a pull request.
The strip-jar goal can be executed without a Maven pom file:
mvn io.github.zlika:reproducible-build-maven-plugin:0.4:strip-jar -Dreproducible.outputDirectory=/tmp