@hundread1800
Hi there. Thank you for confirming you're using sandbox, we understand this population should not drop between saving and loading. This information along with the screenshot provided has been sent to the game team for further evaluation. We'll be sure to let players know when we have any information to share on the investigation.
If you have any other questions, or any details you'd like to add, please let us know!
Thanks again for the help reporting this.