Steps:1
Please check error.log file there you might see some error associated with that clientlib.
When I had issue with minification , I saw error message in error.log file and then I took necessary steps to fix.
Step:2
To troubleshoot the issue please follow the below steps -
a. AEM 6.5 uses following closure-compiler-v20190121.jar for js minification, also highlighted in below screenshot -

b. If we take a closure look , we could see com.google.javascript is part of this closure compiler bundle.
c. Next you can download the bundle:closure-compiler-v20190121.jar from aeminstance\crx-quickstart\launchpad\felix\bundle290\version0.0\bundle.jar-embedded. Bundle ID may vary in your case-

d. To understand the minification issue , you can execute below command to compile the Javascript file -
java -jar compiler.jar --js hello.js --js_output_file hello-compiled.js
Getting Started with the Closure Compiler Application | Google Developers
It may throw error during compilation and it will help you why minification isn't working.
In my project Front End developers do the minification outside as part of the Frontend build process; Front End devs would not rely on the AEM features, because there are better ways and tools to do so.