That widget is set to be category specific. It will only show up if you are on a post in the “review” category. However, I have tried other widgets in that same location without being category specific, and they did the same thing.
As a test, I just added a Goodreads widget. I copied from the Widget page so you can see that the Goodreads widget is in fact set for the primary sidebar, even though it is showing up in a different location on the page:
Primary Sidebar
Edit widget: Blog Subscriptions (Jetpack)
Blog Subscriptions (Jetpack): Subscribe via Email
Edit widget: Search
Search: Search
Edit widget: PayPal Donation Button
PayPal Donation Button
Edit widget: Goodreads (Jetpack)
Goodreads (Jetpack): Jen’s Goodreads
Edit widget: Custom HTML
Custom HTML: Our Rating Scale
I appreciate your help.
~Jen