I am getting this as well. I'm not sure if it has anything to do with it but figured I would add some details about my experience in case it helps you identify why it is occuring.
I am working with a large document, so I've turned off automatic updates. When adding a new citation, the message appears for only a millisecond after I add. When refreshing the document, the message will appear for much longer as Zotero goes over my document.
Glad to hear you're looking into this, no idea if this info helps but best of luck figuring it out!