The only time I've noticed this appears to be intentional. I.e. When riding on a mount. The most obvious example is the long tail on the Ninja AF head gear which moves quite fluidly when on your own two feet but sticks out ramrod straight when mounted.

I would suggest making sure your graphics card driver is up to date. You could also try to repair files via the Config menu in the launcher. If there's a missing or corrupt file causing it then that might fix it. Just a heads up that doing that will likely take some time. Sorry I'm not able to help more.