Image captions not displaying properly

I am working on a localhost site with the latest version of WP, the Atomic Blocks theme and no plugins. When I drop an image from Finder into a new block, type a caption, set image to medium size, and align right or align left, everything displays properly in the editor. But on the front end, the caption is aligned left and is only one or two words wide, with the other words on separate lines.

When I then set the image to aligncenter, the caption displays properly, center-aligned and words on a single line. If I then set the image to alignright or alignleft again, the caption appears on top of the image! Not sure if this is a Gutenberg issue or Atomic Blocks code. I could not find anything in the CSS causing this behavior.

Thank you!