There are a couple problems here. The first is that you are setting both an Edit and a Visibility UProperty for the variable. You are only able to have one or the other in the UProperty list (just an FYI, the EditDefaultsOnly flag includes the VisibleDefaultsOnly tag).
The second issue is that the TSubobjectPtr variable you are implementing the UProperty flags for (if I found the same tutorial that you were looking at) cannot be set to editable, so you will only be able to use the VisibleDefaultsOnly flag.
Can just place a comment in the video at the point. The developer pasted in the code as the video progressed, so I figured it was compiled and work. And it might have worked in the older release, and you guys probably just changed something.