Hey I also have this issue with Vectorworks 2018 (it also happened with 2017) - basically when I'm doing a walkthrough with open GL it seems to cut into objects before I actually reach them.
I've attached an example where I'm at about 1.5m above the floor level and it still cuts through to reveal beneath.
Super annoying!!
Any help would be very gratefully received!
My specs are:
i7-7700k, GTX 1080, 16 GB Ram
Running Windows 10 v1703
Vectorworks 2018