Copy function fails in GCP Cloud Build?

I'm having a strange problem where a Dockerfile builds completely fine locally but fails in GCP cloud build due to being unable to find the source files during a copy statement. I am building a spring jar file from mvn clean package which I can see is successfully completing in the logs and is overwriting the appropriate package within the target/ directory.

Dockerfile

**FROM openjdk:21-slim
WORKDIR /app
COPY . /app/my-project/
# Update the package lists
RUN apt-get update -y
# Install Maven
RUN apt-get install -y default-jdk maven
WORKDIR /app/my-project
RUN ["mvn", "clean", "compile", "-Dspring-boot.run.jvmArguments='-Dspring.profiles.active=stage'"]
RUN ["mvn", "clean" ,"package" ,"-DskipTests=true"]
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} /etc/my-project/app.jar <---- FAILS HERE
EXPOSE 8080
ENTRYPOINT ["java", "-Dspring.profiles.active=stage", "-jar","/etc/my-project/app.jar"]

cloudbuild.yaml

steps:
- name: gcr.io/cloud-builders/docker
  args: ['build', '-t', 'prod/my-project', '.']
options:
  logging: CLOUD_LOGGING_ONLY

.cloudignore This is the latest thing I've tried, since I read somewhere that what is in my .gitignore is somehow being excluded from my cloud build. Having a .cloudignore files supposedly helps in including the target directory but I have not been successful with it.

!target/

Edit .cloudignore I've also tried the following as I saw it in another post with no success either.

!target/**

Failure reason

"COPY failed: no source files were specified"

Log of mvn clean package succeeding

Replacing main artifact /app/my-project/target/my-project-0.0.1-SNAPSHOT.jar with repackaged archive, adding nested dependencies in BOOT-INF/."

I've tried everything I've typed above. I've also tried using a absolute path to the jar file itself with the same type of copy error.