Hey,
Got a similar problem and simulations ends possible due to numerical instability.
What you can do is export just the FW as stp to simscale and simulate it alone, however you wont be able to merge with the rest of the car as we dont have the car in stp.
PS:
Full project(in stl): https://www.simscale.com/workbench?publiclink=4c025800-7f09-4314-ae0f-e39671b4abc0
Only FW(in stp): https://www.simscale.com/workbench?publiclink=74a94ba6-bfaf-471a-81c9-42a0378331d4
Also if I convert the stp to stl the mesh gets better, but still get the same error during simulation.
Conversion test: https://www.simscale.com/workbench?publiclink=649bf6d1-ede4-44bf-a3ef-c6cfaa2d8398
Best Wishes,
Luis Calzado