Issue Site's IIS Worker Process Group has less file permissions on subdomains than on parent domains

[Joel Beazelman]

I created a subdomain beta.xyz.com under the parent domain xyx.com. After installing my ASP.NET Core application in the beta.xyz.com, I received write permission errors when accessing the App_Data. I discovered Plesk uses the same worker process group account, IWPG_xyz, for the parent site and subdomain, but it lacks modify permissions on httpdocs and its subfolders.

First, what's the reason for the different permissions? Is this a bug or is there another reason? Second, what's the best way to correct the permissions on the subdomain such that the permissions stay intact if I need to repair the permissions in the future, update the site, or migrate the files to another server. In the past, I've discovered nasty consequences from changing things behind Plesk's back.