After importing a site backup into a new production machine, we can no longer see previews of attachments. What is strange is that in a previous staging instance in which we performed the same site backup restoration procedure, we can preview the attachments.
We suspect that it may be due to proxies or firewalls, because we had to "substitute" the old production Confluence instance with the new Confluence instance. Could this possibly affected retrieval of file previews? We can see the file thumbnail and we can download it, but previews just won't work.
I found suggestions to enable certain plugins in Confluence, but when I checked, they were all already enabled, so I don't believe it is a plugin problem.