I found the design in question in your account. The fact that the dropout specs didn't match the specs in the BikeCAD database of standard parts wasn't the reason this file didn't load. It actually loaded without issue in BikeCAD Pro. There wasn't theoretically anything wrong with how the seat stays were modeled as a combination of a seat stay and an extra tube. However, for some reason, the free version of BikeCAD was not able to manage this geometry and froze as a result.

I have just redone the seat stays for you. I was able to achieve the same geometry as found in your earlier model by deleting the extra tube and bending the seat stay. You'll find the new model in your My Designs section.