Having NTFS permissions that are messed up is a HUGE headache. Fixing them means trying to trick NTFS into letting you do what you need to, and sometimes it just won’t let you. Below is my nuclear option that will, at least, get you back where you can make the necessary changes to get what you need set.
Download the NTFSSecurity powershell module, unblock the zip file, then extract it to C:\Windows\System32\WindowsPowerShell\v1.0\Modules
Make sure that the top level folder has the permissions you want to inherit. Make sure you have permissions on this top level folder.
Run Powershell as admin.
Run the following commands in the folder you want to propagate inheritance down from:
import-module ntfssecurity
enable-privileges
get-childitem -recurse | Enable-NTFSAccessInheritance