Trees and foliage not visible

[Greg]

Trees and foliage are only visible in scene view. Entering play mode the trees and foliage are invisible but colliders are there. I use 3 different controllers (Invector, HFPS and STP) but get the same outcome with all 3. I have no idea how to fix this but thinking it's a rendering issue. Using Gaia Pro 2021.

[Bryan]

More than likely this is using Flora. 

Which means you would need to use the Gaia Custom Player with your 3rd Party assets. 
Just attach the player and camera to Gaia's Custom Player and you should be good to go.