If you are previewing content prior to publishing and see a notification what "The task Publishing.Preview is currently queued", but your preview isn't starting, it's because to avoid negative effects on your Confluence system's performance, the number of parallel threads used by Scroll Versions is limited to four.
These threads are used by the following tasks:
- Performing a Health Check
- Rebuilding the Scroll Lookup Index
You can only perform up to four of these tasks at a same time – for example, three publishing and one previewing task. If all 4 threads are in use, additional requests are queued and the notification is displayed. Once there's a free thread, the message will disappear and the preview will start normally.