How to sort files in reverse alphabetical and maintain that setting for given folders
Your Finder .plist file may be corrupted. Try the following steps:


Navigate to ~/Library/Preferences (press ⇧ shift ⌘ cmd G in Finder).
Drag com.apple.finder.plist to your Desktop.
While holding ⌥ opt, right-click the Finder icon on your dock, then click Relaunch.


See if Finder now remembers your view preferences for the folder in question. If not, you can drag that .plist back where it was and relaunch Finder again.

Do note that in List view, you have to navigate to the actual folder for its view preferences to apply. A folder expanded from a parent folder will use the view preferences of whatever folder you expanded from.