Did you make sure to remove all registry entries and manually check that the config folders had been deleted before downgrading? That shouldn’t really matter but it’s good practice when trying to troubleshoot. Detailed instructions on that process here:
Seems like you are both on windows, so the easiest and quickest way to debug this is by creating a new User profile and install on that. Don’t use the old project files and instead start a new project with the bare bones minimum required to test for audio issues.
I’m assuming there haven’t been any audio driver updates during your regularly scheduled windows updates?