When you use EndNote's Cite While You Write (CWYW) function to add citations to your document, you are adding a lot of coding to the document to make the citations and references work. If you open your EndNote formatted Word documents in a web-based word processor (e.g. Google Docs, or the web based version of Word in Microsoft Teams / SharePoint / OneDrive) you can damage this coding and corrupt your document.
The desktop app (the Word software loaded onto the hard-drive of your computer) is more stable with EndNote.
It's ok to store your documents in OneDrive, but always open and work with your EndNote formatted Word documents using the desktop app.
This video is for EndNote 20, but there are no significant changes to the Cite While You Write function in EndNote X9.
EndNote's Cite While You Write (CWYW) can also be used with Pages for Mac.
There is a plug-in you can install to make EndNote work with Pages on a Mac.
A video you can watch to get an overview of CWYW for Pages
There is a section in this guide on using EndNote X8 with Apple Pages on a Mac.