After update to 3.3.5 no more images in the folders

One of our customers bought your plug-in (v 3.3.4) and it worked like you promote here. After he updated to 3.3.5 he still can see all (sub)folders but no more images. The images are still on the page and once I disable the plug-in I can see them again in the media library. Is there an issue with the database or any suggestion what he can do?