software bug - scene is 'destroyed'

I am using 3D Stager since 3 years now. Since probably a week I ran into a serious problem (twice). My whole stager scene is not usable anymore.
I can navigate but i can NOT render or delete/add any asset in the scene. Nor can I change anything.
Scene assets are visible in the view port but not on the right side, where I normally see all assets and cams.
To say it short: this sucks!