Don't worry, I am working on a way to serialize/save and backup your projects, but for the moment it is not available. (Soo much to do)
Fixed.
Nothing was lost.
I didn't restore any backup.
I only corrected some JS to do not block on undefined var.
In facts, I think using 2 builders (wich must not be possible, the issue is there), you have broken a FK link or maybe group by property using this key.
So, check very well your project and how the FK are used.
Sorry for inconvenience. And thank you for this notice.