GitLab backup doesn't include wiki

We have GitLab CE 9.1.2 installed on our server where a backup is scheduled to run every 8:00 PM Mon-Fri. So far things are fine but yesterday we started using the Wiki. I double checked the backup file and somehow it had the exact same size as the backup the previous day (nothing was done in the system other than creating Wiki pages).

Because of that I suspected that the Wiki wasn’t included in the backup process so I opened up a VM and tried to restore the backup file. After the successful operation I went over to the Wiki section of the project and it was empty.

I was reading some resources and they say the repo shouldn’t be empty for the Wiki to be included but our repo is full of codes, commits, branches, issues, etc. I followed the backup instructions for the Omnibus installation because that’s what we have.

0 20 * * 1-5 /opt/gitlab/bin/gitlab-rake gitlab:backup:create CRON=1

As you could see I didn’t include any SKIP environment variable so it shouldn’t skip anything. Am I missing something? I followed the instructions properly. Please help me, I need a full backup of the system.