Nemo refuses to access folders

There are folders that appear in my tree view - they even expand to show their sub-folders - but when I click on them Nemo refuses to show any of the files in those folders. The address bar doesn't even indicate that I have clicked on it - it still shows the name of the previous folder I'd been in.
These are folders that Nemo HAS accessed in the past but won't any more, and I have no idea what changed.
Other file managers can still access those folders but Nemo refuses to.
I've been unable to find anyone else who's had this problem, possibly because my search terms are too generic. Any thoughts?