Are ALL the images affected? When you say that all the history has been lost, can you tell me if the history panel is completely blank, of if there's just the one "Import" step showing?
There is a "Clear History" option on the Develop menu, that would result in a completely blank history panel. It only affects the selected images, so to erase the history of all images they must all have been selected when using that option.
If there's still an "Import" step showing, that would mean that the images have been re-imported. Is that a possibility?
Thank you for your response. Yes, all images have been touched, the panel history is empty, the import step does not appear. I didn't use the "clear history" option in the development module. The imported step is not displayed.