Hello,
I've been facing a look-a-like issue but not when playing on workflows.
The reason is that the node is malformed. The following explanation may seem weird but, this is how we resolved it and how it can occure :
- it can occure when there is a problem with the thumbnail creation on the document
- to avoid it, we had (as administrator's rights) to update the document (simple metadata update) or upload a new version on it, then the other users (none administrator users) could see the document back.
Do you have any trace in your log? (when this occures to us, we had an exception thrown, something like "permission's problems or errors")
good luck
Bertrand