As @DanBW has mentioned, we did identify a bug which has now been fixed: Replace/Expire Media: Unable to delete expired media after replacement 路 Issue #3654 路 xibosignage/xibo 路 GitHub
Therefore upgrading to the latest version should fix the issue you are experiencing.
Could I also ask that you try to refrain from creating duplicate posts for the same issue as it makes it harder for the community to keep track when following, I have linked here 
Thank you