Hi all
This morning, after updating my Windows 10 Pro to the latest version (2004), I was unable to access any of my published apps set up using this tool. When I fired up the RemoteApp Tool, all the remote apps were gone. Thankfully I had a backup of the registry entries and after restoring it, my apps came back.
So it looks like Microsoft has started wiping the TSAppAllowList key on certain updates. Workaround is to simply perform a registry backup whenever you make a change, then restore if they "disappear".