Hey @mooniemoon, since this happened several times for you, can you replicate it with exact steps? If so, does this happen only when you open a specific document? How many windows of Zotero do you have open? Is it only one, and you are just closing the current document and open another? Or do you have multiple windows with multiple documents open, and you switch between them.

Finally, can you start recording a debug log, try to reproduce the crash, and when you relaunch Zotero, copy and share the debug log id here?