Collection disappeared
I've used Zotero for a year. I moved to Zotero because I had major issues with Endnote and Mendeley, particularly with stuff disappearing. I just recently had same issue with Zotero. I have several layers/levels of collections in one library. I recently noticed where one second-level collection that had probably two levels within it went blank. The collection folder is still there, just none of the sub-collection or references. Luckily I had a fairly recent backup in another library (I learned my lesson from past) I could use to rebuild it. But, is there any way of figuring out what happened? I am pretty sure it wasn't just user error (accident), since about a half dozen sub-collections disappeared, rather than just one.
Library
Collection
Subcollection Level 1
Subcollection Level 2
Subcollection Level 2
Subcollection Level 2
In this library we have 8 Collections, and each has three Subcollections Level 1, and each of those has numerous Subcollections Level 2. In this case, for this Subcollection Level 1 of interest, all Subcollections Level 2 (I think about six of them) disappeared. The other Subcollections Level 1 under that Collection remained. The references were still in Collection, but no longer in that Subcollection Level 1.