This page lists any changes in 2017.3 which might affect existing projects when you upgrade from earlier versions of Unity.
К примеру:
Changes in data format which may require re-baking.
Changes to the meaning or behavior of any existing functions, parameters or component values.
Deprecation of any function or feature. (Alternatives are suggested.)
Lightmap intensity & emissive Materials in Enlighten
A bug introduced in 2017.2 increased the intensity of lightmaps generated for Scenes with static Meshes that have emissive Materials. This was the same for both baked and real-time emissive Materials. This has now been fixed in 2017.3 so the intensity is now similar to how it was in 2017.1.
This change affects any projects you have built in 2017.2 and then upgrade to 2017.3 or newer.
PassType.VertexLMRGBM has been deprecated
In Unity 2017.3, the shader pass VertexLMRGB is ignored. For example:
Tags { "LightMode" = "VertexLMRGBM" }
Instead, provide or update a VertexLM shader pass using the DecodeLightmap shader function that supports all types of lightmap encodings. Built-in mobile shaders also use DecodeLightmap shader function now.
Lighting output may change in your existing projects that use built-in mobile shaders such as Mobile or VertexLit on desktop platforms. This is because the maximum range of RGBM encoded values has changed from [0, 8] to [0, 5].