Just had a similar event, but isolated to my own account:
1). Logged in, navigated to team drive, create new document, edit new document. Document shows saved in upper left corner.
2). Went to private tab, logged in, navigated to team drive, document is missing.
3). Went back to normal tab, closed everything and logged out. Logged back in, navigated to team drive, opened document. “Syncing changes, please wait” message appears and persists. After about 10 minutes, I close the tab and navigate back to the team drive. The document is gone. Not in team drive, not in trash, not in recents. It’s just gone.
4). I cautiously re-created the doc from scratch, but right after making the new document, went in via private tab to see if I could see the file - it was there. Adding content to the doc in normal tab and confirming updates in private tab showed things working as-expected.
I have no idea what caused the first document to indicate that it had saved properly, but clearly fail to. I also don’t know why the sync process nuked the file entirely.