My wife and I have a number of shared folders, of which we are both Administrators. One of them — and only one — sometimes disappears from her view. To re-enable her ability to see it, I have to remove her permissions from the folder and add them back. The folder shows up for a while, but eventually disappears again and we have to repeat the process. It's always this one folder and only this one folder. Everything else is fine, including multiple other shared folders.