Artifacts not getting copies to path

First of all I am sorry if this issue has been raised before. I am searched the forum extensively as well as google it for two days without success.

I am using the following .gitlab-ci.yml file for building the Android apk:

image: jangrewe/gitlab-ci-android

variables:
  ANDROID_COMPILE_SDK: "28"
  ANDROID_BUILD_TOOLS: "28.0.2"
  ANDROID_SDK_TOOLS:   "4333796"
  JAVA_OPTS: "-Dhttp.proxyHost=<IP> -Dhttp.proxyPort=<Port> -Dhttps.proxyHost=<IP> -Dhttps.proxyPort=<Port>"

before_script:
  - export GRADLE_USER_HOME=$(pwd)/.gradle
  - touch local.properties
  - mkdir apk_release
  - chmod +x ./gradlew

cache:
  key: ${CI_PROJECT_ID}
  paths:
  - .gradle/

build:
  stage: build
  script:
  - ./gradlew assembleRelease
  artifacts:
    paths:
    - app/build/outputs/apk/release/
    expire_in: 12 hours

The runner is using docker and I am see the apk file is created at /var/lib/docker/volumes/614f1779d5e46c61fe84b81d2cb40055eff68eea1bfc291984a6220bf1c19179/_data///app/build/outputs/apk/release/app-release-unsigned.apk

The job output shows: Uploading artifacts... app/build/outputs/apk/release/: found 3 matching files Uploading artifacts to coordinator... ok id=121 responseStatus=201 Created token=Q2QuLFyx Job succeeded

However, when I press the download button, an empty archive is downloaded. The apk is not getting moved to the right artifact directory so that it can be available through the gitlab interface.

I am using Gitlab community version 11.8.2. Any help will be really appreciated. Thank you very much.