I discovered the issue some time ago. I apologize for not posting the solution.
Here’s how I fixed mine.
So you probably tagged the new version and set that version as the stable tag in both the trunk and the mentioned tagged folder, BUT
You still need to change the version number in your main plugin file.
For Random Quotes, the main plugin file is rq.php. Once I changed the version in that file, it updated within 15 minutes.
Hope this helps.