Rush App stopped saving progress

Using Rush app on my iPhone. The app and my phone are all up to date in terms of software updates etc. I've been using successfully for several years so know what I'm doing. Suddenly it has stopped saving progress completely. I have a project that I did several hours work on. I exited the app and went back in later and none of the changes had been saved. I don't get it! It auto saves, so where is my work? I have tried several times and the same thing happens each time. I've tried restarting my phone, making sure im not out of storage, checked for app updates etc but nothing works. So I cannot do any editing with this app I'm paying for because nothing saves!