Hello! I have seen this asked several times, and none of the solutions have helped me so far.
I am having an interesting experience where when I go to add the asset from my UE Library to a new game, the folders in the content browser are empty… But when I look at the actual files on my drive using File Explorer, they are there. Why are they not showing? This is occurring on versions 4.26 and 5.0. To give you an idea of what I am talking about, here is a little video: Lockpicking Problem - YouTube
I noticed that you are still using 5.0 Early Access. Updating to 5.0.2 should resolve this.
You’re seeing this error because assets created with a later version of the engine cannot be opened in an earlier version. So for example those “Lockpick System” assets were created in 5.0 (Release) and cannot be opened with 5.0 (EA/Prerelease)
On thing you could do that solve file related issues to sometimes is right-click in the folder in the content browser and select “Fix up redirectors in folders”.
The same problem, UE4.27. I closed Content browser, and opened Content browser2 through the menu. All the content appeared.