Annotations on static page being rendered as orphans

## Bug report form
### Steps to reproduce
1. Join this group:

https://hypothes.is/groups/KggbKjaG/f2017-p0-us-history

2. Open this page:

http://www.bbc.com/news/world-asia-41158281

3. Activate extension, toggle to group

### Expected behaviour
I should see the group's annotations.

### Actual behaviour
Sometimes for a second, sometimes for much longer, the groups annotations are rendered as orphans (though this is a presumably relatively static page)

### Browser/system information
Latest Chrome, Chrome extension.

### Additional details
The problem seems worse when linking from the group home page to a specific annotation and then viewing all annotations

Reproduce the issue in the Chrome extension using the linked group and BBC page, first opening the page directly and then following a specific annotation from the group home page. Compare the annotation state while switching to the group; done means the group's annotations appear normally without being rendered as orphans.

Written by the indexing model from the issue text.