Visualforce page is not saving and closing like it used to. It was created on 04/2016, and was last edited 09/2016. It has been working fine until today. I don't know how to code as we hired a consultant to do this page last year. I need some help troubleshooting.
Thank you in advance! 
Liz 

So maybe I'm missing something here, but I was working through the Create and Customize List Views section of the Lightning Experience Customization and the Challenge section is missing. I tried logging out, then back in and checked several browsers with no luck. Anyone else experience this problem. Here's a screenshot: