Despite performance improvements with the 10.11.x release, many users report issues related to collections. Hopefully these issues will be addressed soon by the Jellyfin developers, until then some of you (but not all) might have the following issues.
- Slow UI Loading: The main Collections tab often takes very long to populate. Interesting reply here.
- Visibility Bugs: Collections may appear within library folders but remain missing from the dedicated sidebar.
Overarching issue to follow is here.
It's been confirmed that the fix will be included in the next major release.