Disappearing Highlights

### Steps to reproduce
1. Annotating on this article: https://www.newyorker.com/magazine/2017/12/18/jim-simons-the-numbers-king#annotations:mulVSOFoEeegQ08srVLWLg
2. Created a number of highlights, but then when I created another one the previous ones disappeared.
3. Those previous highlights did not show in my activity page. I was able to highlight the rest of the page normally.

### Expected behaviour
Tell us what should happen.
Highlights should stay.

### Actual behaviour
Tell us what happens instead.
Highlights disappeared

### Browser/system information
Tell us which browser, browser version, and operating system you were using when
you encountered this issue.
Chrome Version 63.0.3239.84

### Additional details
If you have other information which might be helpful, please include it. If a
screenshot will help to illustrate the issue you are reporting, please include
one.