disappear

When I am in hammer some blocks will disappear and reappear while I am flying around and it is kind of annoying because sometimes I go to texture stuff and it will disappear when I go to apply the texture. Does anyone know whats going on.

I wanted to do a little bit of displacements to let a area in the skybox not look so weird but when I run the map its gone! Is Can be because of leaks but i don't know Does somebody know whats wrong?

Hey guys, I've been having an issue with a recent map I've been working on where displacements will disappear. I can create displacement brushes, but as soon as I modify the displacement, it will disappear ingame. I'm just simply using a medium-sized level 3 displacement that seems not to work...