Hi Thanks for replying. I'm running the latest version. Have tried disable all sorts of things, restarting app and iPad without any results. Actually as mention before I want to flatten the project in the first place, but it can't be flatten, the process just keep going, it never finish. I've tried to merge layers, with the same result. I've tried to use "save as" to save the file without the histories, but once I have saved it in my Google Drive. The file is not recognised by the app, cannot be open at all. What I have succeeded so far is resizing the project into a lower resolution and then I have no trouble flattening the project. This make me wonder, what is the maximum resolution is supported by the app? Does it means I need to resize the images everytime I start a project first?