Both proof.subject-7.com and platform.subject-7.com point to the exact same server.
If this is not a mistake and this is really the case, remove all local installations and down from https://platform.subject-7.com. Avoid using https://proof.subject-7.com.
However, if you meant having an on-prem installation and the SaaS version on the same machine, you need to make sure you use 2 different installation folders. here is what I would do:
1. Uninstall all current Local Player installations
2. Browse to https://platform.subject-7.com and download the local player installation package
3. Start the installation and when prompted for the directory/folder of installation make sure you use a specific name like Subject7Cloud and make sure you don't use the default name
4. Do the same steps 1 to 3 above for on-prem installation but make sure in Step 3 you provide A DIFFERENT name for the folder such as Subject7OnPrem (or whatever makes sense in your project, but just not the default name)