We are working hard to fix that issue. The work around at this time is to roll back your nVidia driver or play in the 32 bit mode on Steam.
Devon sent me this message:
The problem still exists, even with the latest driver hotfix version 353.12.
I'm still working on this issue locally, and we've also been communicating
with Unity and NVidia. Non-technically speaking, it's like trying to catch a
greased pig while blindfolded, only the pig randomly warps to another field,
or disappears completely whenever you put on gloves, or peak out of your
blindfold, or even listen for pig noises.
Users who want, or need to run with the latest NVidia drivers can continue
to do so as long as they run the 32bit version of TGC. (Available under the
Beta options in Steam.)