Same problem, Background images do not show up, all the formating inside generate blocks do not show up in the preview page. On the backend everything is visible. I have the latest version of both generate press and generate blocks…
I figured out that it was an AMP plugin (by AMP Project Contributors) conflict with Generate Blocks. Once I deactivated the plugin the Container Background image works. Not sure if this is something Generate Blocks would like to look into or if it’s more an issue with the way the AMP plugin is built. Let me know and I can flag it with AMP Project Contributors if it’s an issue on their side.