Content is not saved- progress lost

I have spent quite a while creating interactive book-with  image hotspots. I saved it and preview, it looked fine, and then I edited further, added more columns and as soon as I clicked on "save" button on top right, and directed to preview page, I see there was no content- I went back to the "edit" mode and there also were no content at all....

I'm in the trial account and was considering to purchase a subscription but if this is a reoccuring bug, its quite unconvenient!