This version is very outdated. There’s a very good chance that your issue has been fixed since then.
Please upgrade to:
<gatling.version>3.9.5</gatling.version>
<gatling-maven-plugin.version>4.3.7</gatling-maven-plugin.version>
Make sure to check the official demo project for maven + Scala.
If you still experience an issue after upgrading, please provide a reproducer so we can investigate, see How to Ask a Question.