Mixing Gum and 3D

Introduction

Gum draw calls can be performed at any point in your game's Draw method. You can have Gum draw above or below 3D objects by moving the GumUI.Draw() call.

XNA-Likes (MonoGame, FNA, KNI) and Draw

The GumUI.Draw() call internally uses a SpriteBatch to draw all UI. SpriteBatch can modify render states in a way that can break 3D rendering, such as by drawing Model instances, or the various GraphicsDevice draw calls.

You can verify that these state changes are breaking your 3D rendering by temporarily commenting-out GumUI.Draw(). If this is in fact the problem, you can restore the GraphicsDevice settings after the draw.

An older article by Shawn Hargreaves states:

So exactly which states does SpriteBatch change? Here's the complete list:

    GraphicsDevice.BlendState = BlendState.AlphaBlend;
    GraphicsDevice.DepthStencilState = DepthStencilState.None;
    GraphicsDevice.RasterizerState = RasterizerState.CullCounterClockwise;
    GraphicsDevice.SamplerStates[0] = SamplerState.LinearClamp;

SpriteBatch also modifies the vertex buffer, index buffer, and applies its own effect onto the GraphicsDevice.

Before you draw anything in 3D you will probably want to reset these states:

    GraphicsDevice.BlendState = BlendState.Opaque;
    GraphicsDevice.DepthStencilState = DepthStencilState.Default;

Depending on your 3D content, you may also want to set:

    GraphicsDevice.SamplerStates[0] = SamplerState.LinearWrap;

For more information see this article: https://shawnhargreaves.com/blog/spritebatch-and-renderstates-in-xna-game-studio-4-0.html