Thumbnails in DT not visible

Hi. I’m using DT 3.7.2 on MacOS 11.2.3. I have noticed that the thumbnails for many PDFs are not available. I tried to generate them manually but without success. Is this a known problem for others too?

Are the PDF documents encrypted? Or does updating to macOS 11.5.1 fix this?

It has taken a little time to do the Update to macOS 11.5.1… now I was able to install it…

The PDF documents are not encrypted and the updating to 11.5.1 does not fix the issue.

Could you please send such a document to cgrunenberg - at - Thank you!