Context classloader and issue with loading resource within one of the dependencies

Question

I'm facing one odd issue with loading a properties file from a static class/method which is inside a jar file. This jar file is part of a spring boot application. So basically following is the structure

API-springboot.jar
|
|---- BOOT-INF/lib/my-other.jar
      |
      |----- app.properties
      |----- com/foo/bar/blah/Utils.class --> Static class loading app.properties

• Here Utils.class is a collection of various static utility methods.
• Util.class has a static method which loads the app.properties. Below is the code of Utils

package com.foo.bar.blah;

public final class Utils {
    private static final String PROPS_FILE = "app.properties";
    private static final Properties props = loadProperties();

    public static String doSomething(String str) {
        // ... some logic by reading props
        return "blah";
    }

    private static Properties loadProperties() {
        LOG.debug("Loading properties {}", PROPS_FILE);
        InputStream resourceAsStream = Thread.currentThread()
                .getContextClassLoader()
                .getResourceAsStream(PROPS_FILE);

        if (resourceAsStream == null) {
            throw new RuntimeException("Can't load the properties file " + PROPS_FILE);
        }

        Properties properties = new Properties();
        try {
            properties.load(new InputStreamReader(resourceAsStream, StandardCharsets.UTF_8));
        } catch (IOException e) {
            LOG.error(e.getMessage(), e);
            throw new RuntimeException(e);
        }

        return properties;
    }
}

• Now when the Utils.doSomething is invoked for the first time, loadProperties will be invoked and load app.properties (at the root of the classpath)

• This works fine locally (macOS & OpenJDK 11.0.8) and also on my test env (RHEL 7 and OpenJDK 11.0.9)

• When deployed on UAT env, it cannot find app.properties and throws an exception as defined in the method

    if (resourceAsStream == null) {
        throw new RuntimeException("Can't load the properties file " + PROPS_FILE);
    }

• Spring boot version is v2.3.5.RELEASE

• Below is what I've checked till now

  • On UAT, I have the same JRE as on test
  • UAT and test has the same version of the application deployed via CI/CD pipeline (Jenkins/Artifactory etc)
  • On UAT, I extracted my application's spring-boot jar file and can see the my-other.jar under BOOT-INF/lib
  • I verified that my-other.jar has the app.properties in the root and also the Utils.class is present
  • I created a sample test class on one of the UAT servers which simply calls Utils.doSomething("blah") with correct classpath set and it can load the app.properties from the jar and shows expected result. But the issue comes when it's invoked from the spring-boot application.
  • JRE version is the same on UAT and test and spring-boot application is using the right JRE.

    openjdk version "11.0.9" 2020-10-20 LTS
    OpenJDK Runtime Environment 18.9 (build 11.0.9+11-LTS)
    OpenJDK 64-Bit Server VM 18.9 (build 11.0.9+11-LTS, mixed mode, sharing)

Question: What is causing this behaviour? Am I missing anything? Spent 3 hours with no success.