Hi. Many hours of work seem not to have been saved. The tail section of my airplane is missing after closing Shapr3D for half an hour and then returning to it. Searching through the history I can see the outline of the tail (in red) but I have no idea hopw to recover it.
Seems like you have an error with the base sketch of your part. You may have accidentally deleted it. You can delete the „Deletion“ Action with which you deleted your sketch and it should work.