I don't see the option to unshare a folder, even though I'm the owner

I am having exactly this same problem.  The folders where the "unshare" button does not appear are both folders where 1) I am the owner; 2) there are no nested shared folders; and 3) the folders themselves are not nested within shared folders.  I have tried dropbox support to no avail (they repeatedly asked me to do things I had already clearly told them I had already done, asked me to repeat information about 3 or 4 times, and then marked the ticket as "solved" despite never addressing my issue at all).  

(Beyond this issue, allowing us to share folders within shared folders, but then never able to unshare either folder again in future, is horrible design and something that every user should be warned about BEFORE they share any folder within a shared folder.  I recently had to redo my dropbox and lost literally dozens of hours of my time "unsharing" folders because every time I had to 1) click every single subfolder of a subfolder of a subfolder of a subfolder subfolder in a series of thousands of nested files to find the shared ones (there is no way for dropbox to tell you which subfolder is the problem preventing unsharing); 2) drag the child folder elsewhere, completely destroying my folder structure, and wait minutes or hours for it to sync completely; 3) note down by hand where the folder goes back to when I am done so that I don't lose track; 4) unshare the child folder in its new temporary location, waiting minutes or hours for this change to fully sync; 5) drag that child folder back to its original location, waiting minutes or hours for it to fully sync.  And then even after doing all of that, dropbox would often duplicate the folder so that I now had two separate (complete? incomplete? identical? one with missing files? no way to tell!) identically named folders, one in the "new" (original) location, and one in the place I had temporarily dragged it to in order to unshare it--so then I had to manually delete this duplicate copy and hope I had not lost any files in the process.  This is a complete and total disaster--a huge waste of my time, and now I have no idea if all my files made it back to where they belong, or got lost during the copy process.  This process is equally bad whether using the desktop app, the mobile app, or the online web interface inside the browser [I tried them all].  I am now seriously thinking, after almost two decades as a dropbox user, of jumping ship to another platform.)