Here is how it is displayed.
The generation of thumbnails needs some time - maybe you were to fast :-)
The first call for a thumbnail triggers its generation (mode=queued). If you refresh a age after a short time, you will be see the generated thumbnail.
Do the documents really have thumbnails? Can you see the thumbnails when you browse them via share/normal folder?
If not - is there a conversion path form the mime type of your documents to then thumbnail (ex. pdf-->png)?
I see that the issue got resolved itself. Don't know the reason.
No, we don't have a conversion path.
Retrieving data ...