I get this problem every now and then with imported parts. Normally have to reload or redo some work.
In this case I have redrawn the part because it had fallen over and then erased the original imported file.
So it’s a Zw3d model now, after programming it had happened again. In this case I can roll back the design tree and regen each feature to get my work back.
Are others having this problem, any solutions?