@weswitt We were bitten by that too! Assumed it was broken.
All the other default WP themes have a preview thumbnail, so you assume twenty nineteen also would look like the theme thumb – like twenty seventeen.
So as soon as you install or activate you assume the images are missing or a CSS issue. Guess it just mirrors the whole experience of the 5.0 WordPress release ??
I personally even checked Apache logs, turned on debug, put browser in developer mode. Goes to show you something felt missing and broken. Still does. I don’t know what happen to WordPress, but since 5.x just not the same awesome feeling. Sad really.