Hmmm, does this crash happen when you do something specific, or just right before round 20? Which platform are you on (e.g. web/android/PC)? There's a known bug [which will be fixed next release] where placing a junction causes a crash; could that have been it?
Is there a particular block you're right-clicking that causes the crash? I really have no idea what this could be caused by, so I'll see if I can implement an error reporter later.
