Thumbnails not showing up

Just downloaded the widget and put it in my right sidebar. I have posts with 1 image each.
I have changed all of the different combos of show first image, show default image, etc. At first I got a grey box next to my post title. Now I get nothing.
I have tried making an image a featured image, I have tried putting a default image in, still nothing. I’ve saved each time.

Take care,
Jennifer

https://wordpress.org/plugins/recent-posts-widget-with-thumbnails/