I know whats wrong with the Ruiner, and why some cars crash the game,. It’s this:
That is the animation set used on the car, its not included in FiveM, so change it to what the default Ruiner uses:
This will fix a lot of your cars by using animation files that are similar to native cars.
Also, use default weapon hashes for vehicle weapons, there are plenty that could replace the Ruiner’s weapons.
My guide will help you if needed: [How-To] Create/modify your own add-on car
And feel free to ask questions, I will help solve problems when ever I can.
DON’T forget to change the flags in the vehicles.meta to get rid of the ones that are not supported: