Layout problem with gallery of up to 12 items -- text on top

I've tried the page display with 3 templates with same result: 4 images on top row; the 2nd row begins with two empty places followed by 2 images; 4 images on 3rd row and 2 images beginning the last row. Cannot see any CSS reason the left float is not working to arrange the images properly.
In general settings the thumbnails are configured to 200.

Needed to add a clear both. OK now.

The editor will not let me use the br tag in the image caption editor. Is there a way to do a clear:both without changing the CSS. If not is there a suggestion on how I can do this.

It could be the size and/or length of the captions that is throwing off the float layout.

In the caption editor, if you click the HTML button, you can mark up your text but you cannot change the CSS for the template.

If you wish to edit the CSS for the exhibit layout, you can do so within the Exhibit Builder plugin's views: views/shared/exhibit_layouts/gallery-thumbnails/layout.css