Problems with loading gltf on cesium 1.56.1

1. A concise explanation of the problem you're experiencing.

RuntimeError: Fragment shader failed to compile. Compile log: ERROR: 0:81: 'undefined' : undeclared identifier
ERROR: 0:81: 'texture2D' : no matching overloaded function found
ERROR: 0:81: 'SRGBtoLINEAR4' : no matching overloaded function found
ERROR: 0:81: '=' : dimension mismatch
ERROR: 0:81: '=' : cannot convert from 'const mediump float' to 'highp 4-component vector of float'
ERROR: 0:188: 'undefined' : undeclared identifier
ERROR: 0:188: 'texture2D' : no matching overloaded function found
ERROR: 0:188: 'rgb' : field selection requires structure or vector on left hand side
ERROR: 0:188: 'SRGBtoLINEAR3' : no matching overloaded function found
ERROR: 0:188: '=' : dimension mismatch
ERROR: 0:188: '=' : cannot convert from 'const mediump float' to 'highp 3-component vector of float'

Error
    at new RuntimeError (webpack-internal:///./node_modules/cesium/Source/Core/RuntimeError.js:42:19)
    at createAndLinkProgram (webpack-internal:///./node_modules/cesium/Source/Renderer/ShaderProgram.js:230:23)
    at initialize (webpack-internal:///./node_modules/cesium/Source/Renderer/ShaderProgram.js:451:23)
    at ShaderProgram.get (webpack-internal:///./node_modules/cesium/Source/Renderer/ShaderProgram.js:113:17)
    at getAttributeLocations (webpack-internal:///./node_modules/cesium/Source/Scene/Model.js:2489:47)
    at eval (webpack-internal:///./node_modules/cesium/Source/Scene/Model.js:2703:42)
    at Function.ForEach.meshPrimitive (webpack-internal:///./node_modules/cesium/Source/ThirdParty/GltfPipeline/ForEach.js:237:29)
    at eval (webpack-internal:///./node_modules/cesium/Source/Scene/Model.js:2700:21)
    at Function.ForEach.object (webpack-internal:///./node_modules/cesium/Source/ThirdParty/GltfPipeline/ForEach.js:47:29)
    at Function.ForEach.topLevel (webpack-internal:///./node_modules/cesium/Source/ThirdParty/GltfPipeline/ForEach.js:66:24)

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you're using, your operating system and browser.

Can you share the glTF model that’s causing this crash?