Getting lots of these errors in the unity console. Here are some simple steps to reproduce the errors.
  1. Create new unity project in 2019.4.31f1
  2. import latest VRC SDK for worlds (VRCSDK3-WORLD-2021.11.24.16.19_Public)
  3. open Udon Example Scene
  4. select any object in the hierarchy
  5. create a new udon behavior component
  6. open the udon graph
  7. add a variable for an UdonBehavior[]
  8. add a reference to the new variable in the graph
  9. add the array get graph node
TypeResolverException: Type referenced by 'VRCUdonUdonBehaviourArray' could not be resolved.
VRC.Udon.UAssembly.Assembler.UAssemblyAssembler.CreateUninitializedDataVariable (System.String dataVariableName, System.String typeString) (at <b45aa2c5f8b540baba60e42ec85f5c1c>:0)
VRC.Udon.UAssembly.Assembler.UAssemblyAssembler.VisitDataDeclarationStmt (VRC.Udon.UAssembly.Parser.Stmt+DataDeclaration stmt) (at <b45aa2c5f8b540baba60e42ec85f5c1c>:0)
VRC.Udon.UAssembly.Parser.Stmt+DataDeclaration.Accept (VRC.Udon.UAssembly.Parser.Stmt+IVisitor visitor) (at <b45aa2c5f8b540baba60e42ec85f5c1c>:0)
VRC.Udon.UAssembly.Assembler.UAssemblyAssembler.VisitBlockStmt (VRC.Udon.UAssembly.Parser.Stmt+Block stmt) (at <b45aa2c5f8b540baba60e42ec85f5c1c>:0)
VRC.Udon.UAssembly.Parser.Stmt+Block.Accept (VRC.Udon.UAssembly.Parser.Stmt+IVisitor visitor) (at <b45aa2c5f8b540baba60e42ec85f5c1c>:0)
VRC.Udon.UAssembly.Assembler.UAssemblyAssembler.Process (VRC.Udon.UAssembly.Parser.Stmt statement) (at <b45aa2c5f8b540baba60e42ec85f5c1c>:0)
VRC.Udon.UAssembly.Assembler.UAssemblyAssembler.Assemble (System.String assembly) (at <b45aa2c5f8b540baba60e42ec85f5c1c>:0)
VRC.Udon.EditorBindings.UdonEditorInterface.Assemble (System.String assembly) (at <1963e50294534d109b013282bf0faf6c>:0)
VRC.Udon.Editor.UdonEditorManager.Assemble (System.String assembly) (at Assets/Udon/Editor/UdonEditorManager.cs:347)
VRC.Udon.Editor.ProgramSources.UdonAssemblyProgramAsset.AssembleProgram () (at Assets/Udon/Editor/ProgramSources/UdonAssemblyProgram/UdonAssemblyProgramAsset.cs:82)
UnityEngine.Debug:LogException(Exception)
VRC.Udon.Editor.ProgramSources.UdonAssemblyProgramAsset:AssembleProgram() (at Assets/Udon/Editor/ProgramSources/UdonAssemblyProgram/UdonAssemblyProgramAsset.cs:90)
VRC.Udon.Editor.ProgramSources.UdonAssemblyProgramAsset:RefreshProgramImpl() (at Assets/Udon/Editor/ProgramSources/UdonAssemblyProgram/UdonAssemblyProgramAsset.cs:36)
VRC.Udon.Editor.ProgramSources.UdonGraphProgram.UdonGraphProgramAsset:RefreshProgramImpl() (at Assets/Udon/Editor/ProgramSources/UdonGraphProgram/UdonGraphProgramAsset.cs:62)
VRC.Udon.Editor.ProgramSources.UdonProgramAsset:RefreshProgram() (at Assets/Udon/Editor/ProgramSources/UdonProgram/UdonProgramAsset.cs:106)
VRC.Udon.Editor.ProgramSources.UdonProgramAsset:RunEditorUpdate(UdonBehaviour, Boolean&) (at Assets/Udon/Editor/ProgramSources/UdonProgram/UdonProgramAsset.cs:82)
VRC.Udon.UdonBehaviour:RunEditorUpdate(Boolean&) (at Assets/Udon/UdonBehaviour.cs:200)
VRC.Udon.Editor.UdonBehaviourEditor:OnInspectorGUI() (at Assets/Udon/Editor/UdonBehaviourEditor.cs:164)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)
NullReferenceException: Object reference not set to an instance of an object
VRC.Udon.Editor.ProgramSources.UdonProgramAsset.DrawInteractionArea (VRC.Udon.UdonBehaviour udonBehaviour) (at Assets/Udon/Editor/ProgramSources/UdonProgram/UdonProgramAsset.cs:122)
VRC.Udon.Editor.ProgramSources.UdonGraphProgram.UdonGraphProgramAsset.DrawProgramSourceGUI (VRC.Udon.UdonBehaviour udonBehaviour, System.Boolean& dirty) (at Assets/Udon/Editor/ProgramSources/UdonGraphProgram/UdonGraphProgramAsset.cs:48)
VRC.Udon.Editor.ProgramSources.UdonProgramAsset.RunEditorUpdate (VRC.Udon.UdonBehaviour udonBehaviour, System.Boolean& dirty) (at Assets/Udon/Editor/ProgramSources/UdonProgram/UdonProgramAsset.cs:85)
VRC.Udon.UdonBehaviour.RunEditorUpdate (System.Boolean& dirty) (at Assets/Udon/UdonBehaviour.cs:200)
VRC.Udon.Editor.UdonBehaviourEditor.OnInspectorGUI () (at Assets/Udon/Editor/UdonBehaviourEditor.cs:164)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass58_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <a259d3c004024353a2c217da97495055>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)