InDesign Publish Online — Toggle Buttons

We have been using Adobe's Publish Online tool for a few years to publish the digital versions of our magazines and PDFs. A few months ago, the "Toggle Thumbnails" feature suddenly stopped working effectively. The scroll arrow goes away, so you're not able to flip through pages that extend beyond visible view. This is a problem on multiple browsers, on different computers, and in different states. We have tried creating documents from scratch and using templates, and yet the problem persists. This leads us to believe this is an Adobe issue, not something we are doing wrong on our end. Especially because the feature was working fine and then suddenly stopped. 

I have chatted with Adobe and requested call backs and they of course won't take responsibility, and keep trying to diagnose this as an issue on our end. If anyone else is having this problem, please let me know.