Why did my published website revert to image and text placeholders?

I created this website using the new Publish feature, and it was up and running fine. Today I came back to the platform and saw a lot of image placeholders and placeholder text where everything had been set up properly. I am not sure what happened, but since I can't check any sort of history or saved versions, I asked the agent for help recovering what was there before, and it did a great job. Do you know why this happened?