What version are you running?
5.0.5
What's the URL of the page containing the problem?
https://www.reviewboard.org/docs/manual/latest/admin/installation/docker/#file-system
What steps will reproduce the problem?

Follow documented steps to use a custom user and group id for the reviewboard user when installing with docker.
Check the owner and group of the files in the site/ directory.

What is the expected output? What do you see instead?
Expected to see the user matching the configured user/group id. You will see a different user.
What operating system are you using? What browser?
N/A
Please provide any additional information below.
From looking through the source code, it looks like the properties mentioned in the documentation are docker build arguments (ARG). Build arguments can only be used when building the container.

The logic to create the reviewboard user/group either needs to be moved to docker-entrypoint.sh, or add additional logic to docker-entrypoint.sh to change the user/group id if the properties are present.