Hi @Pascal5C1C! We are not able to diagnose working files directly on the forum website. Can you email the Stager scene file and log file that you are seeing the masking issue in to Substance3d-bugs@adobe.com so we can investigate. If the file is under 20 MB you can attach it directly to the email. If it's larger, you can send via a file transfer link like Creative Cloud assets, Dropbox, We Share, One Drive, Google Drive, or similar.
Thanks a lot for the responses. Here are 2 Screenshots. One before rendering - and one after rendering in photoshop. The background is displaced - you can still see some clouds - but the ground is gone.