If you're on the desktop browsers, please try clearing out the cookies/cache for the tool by doing the following.
Firefox
- hit f12
- click on the storage tab
- expand the cookies menu item on the left
- right click on //stevenaleong.com
- click on "delete all"
- reload the page
Chrome
- hit f12
- Click on the applications tab
- expand the cookies item under storage
- right click on //stevenaleong.com
- click "clear"
- reload the page
Once all that is done and the page has been reloaded, try relogging back in/authenticating with spotify and shuffling after that.
Hopefully that should get the shuffler working again. If the playlist still isn't being shuffled, please try creating a new playlist and copying over all the songs into that one.
Otherwise, if that doesn't work, can you please let me know what you're attempting to use the tool with what device/browser/etc.