Missing parts or invisible vehicles are a problem of video driver settings and/or sim settings.
Try this:
- Update your video driver
- Reset your video driver settings to default
If that doesn't work, be sure that:
- The is NOT running into "Compatibility" mode, like XP or Windows 7 compatibility under Windows 8 or 10. This will cause video driver bugs and also slower performances.
- No other addon that starts with the sim runs into "Compatibility" mode.