I also tried selecting hierarchy and marking it as an asset, does not work.
Did I miss something?
Also my asset library works OK on the first time I create a new file and use it. When I reopen that file to continue my work, the asset library is empty... Any tips on that?
Does this help you:
https://cgcookie.com/community/13830-tree-and-leaves-component-separated-after-mark-as-asset-library
maybe?
aaivakic In the asset browser window, on the left menu, try changing the show asset dropdown to all.
If this doesn't help, make sure you are saving your assets correctly,
Mark as asset in outliner,
the save location file path is correct in the preferences, under the file paths tab,
And make sure you save the .blend file in the same asset library folder as in the preferences.
Again, most importantly,
The Blender file with the asset(s) must be saved in the Asset Library folder.