try to use wood-frame for BEGIN of build your car.
first use wood frame
after connect to wood-auto your steel frames and all be ok.
at least about six months ago, when this error popped up, I likewise bypassed this problem. just beginning to build a car starting with a wooden frame and then attaches to the steel and it was all ok. but when I started to build cars with a steel frame - have mepnya and cars did not appear and the frame disappears. Such are the cases. try. It can be a wooden frame remains “untouchable” for the error and the game will create you a car.
yes i not fix this problem but i found some-about bypass and it been ok for me.
after that - i mean you GET your car of one wood-frame, and after connecting to this errr (let’s name it CREATURE) your steel frame - simply remOve your wood frame. voila! your car is will be maked from steel