I've received the same error multiple times while trying to edit this design. The first time it happened I was scrubbing through a video to split it. I haven't been able to edit any designs in the project since.
Apologies for the late response and also for the frustration & difficulties you faced with the new Adobe Express. Do you still see the issue with the design being unable to load due to a network issue? Which browser are you using?
Have you tried using the other suggested browsers (Safari, Microsoft Edge, and Google Chrome) to see if it makes a difference? Try clearing the browser's cache and cookies to check if that helps.
Also, try restarting your computer.
Please let us know if this helps. Also, helps us with a screen recording of the workflow to investigate further.