Can't save? Even when you click on the button to activate persistence? And then after reboot everything disappears? The data file of your Gmod server is empty?
This is a technical administration problem not caused by the scripts.
To solve this permission problem, contact your technical administrator. Or ask for user permission to write to your data folder.

1. Why do I have this problem?
2. Where to find the path to the data folder on Gmod?
3. Useful links for Windows or Linux server permission
4. Conclusion and responsibility

1. Why do I have this problem?
For security reasons it is not recommended to use the root account on a server. It is then necessary to create a user account, except that this user account does not have the right to write by default, it is then necessary to give him the right to write. And this step is sometimes neglected.

2. Where to find the path to the data folder on Gmod?
You will find the data file on your Gmod server at this location : /Steam/steamapps/common/GarrysMod/garrysmod/data

3. Useful links for Windows or Linux server permission
If you do not have an administrator who manages the technical part of your server, these links are from my own research, they are reliable and will meet your needs:

A simple search on Google with these keywords could help you: Permission + Right + File + The name of your operating system.

Permission management for Windows Server
Permission management for Linux

4. Conclusion and responsibility
I am not the technical administrator of your server nor the owner, so I don't have the power to give you the rights if you are not the administrator or if you don't have access to your server.

You now know the main source of the problem, all I can do is this documentation to support you.