mesh does not work in the game

Can someone explain to me why the game does not accept some meshes? the mod works, then I add a mesh even using attach and the mod does not work, when removing the mesh the mod works again, I would like an explanation of what I can change in the mesh for it to work in the game
This happens in the mudrunner, in the spintires it works but on leaving the game and back it does not work anymore

The game does not like individual meshes above 30k. It sounds like when you are adding this mesh it might be going over that limit.

@spun 28k polygonal
also check if you dont have flotating vertexs (dots in the meshes that doesnt connect to anything)

@forces I have had no problems with meshes 29k

Actually the mesh had 55k, I separated some parts and it worked, with little more than 29k error occurred, so I left with 28k and it was ok
Thank you for the tips