Unity 2017.1.2f1: Could not load assembly 'UnityEngine.CoreModule'

[zakarntson]

We upgraded from Unity 5.6 to Unity 2017 and are now getting the following crash:

JsonSerializationException: Could not load assembly 'UnityEngine.CoreModule'. Newtonsoft.Json.Serialization.DefaultSerializationBinder.GetTypeFromTypeNameKey (TypeNameKey typeNameKey) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/DefaultSerializationBinder.cs:82) Newtonsoft.Json.Utilities.ThreadSafeStore2[Newtonsoft.Json.Serialization.DefaultSerializationBinder+TypeNameKey,System.Type].AddValue (TypeNameKey key) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Utilities/ThreadSafeStore.cs:66) Newtonsoft.Json.Utilities.ThreadSafeStore2[Newtonsoft.Json.Serialization.DefaultSerializationBinder+TypeNameKey,System.Type].Get (TypeNameKey key) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Utilities/ThreadSafeStore.cs:58) Newtonsoft.Json.Serialization.DefaultSerializationBinder.BindToType (System.String assemblyName, System.String typeName) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/DefaultSerializationBinder.cs:142) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ResolveTypeName (Newtonsoft.Json.JsonReader reader, System.Type& objectType, Newtonsoft.Json.Serialization.JsonContract& contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, System.String qualifiedTypeName) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:802) Rethrow as JsonSerializationException: Error resolving type specified in JSON 'UnityEngine.Vector3, UnityEngine.CoreModule'. Path 'args.$values[1].CasterHotspotLocation.$type', line 1, position 690. Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ResolveTypeName (Newtonsoft.Json.JsonReader reader, System.Type& objectType, Newtonsoft.Json.Serialization.JsonContract& contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, System.String qualifiedTypeName) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:806) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ReadMetadataProperties (Newtonsoft.Json.JsonReader reader, System.Type& objectType, Newtonsoft.Json.Serialization.JsonContract& contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, System.Object existingValue, System.Object& newValue, System.String& id) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:752) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject (Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, System.Object existingValue) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:459) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal (Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, System.Object existingValue) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:293) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ResolvePropertyAndCreatorValues (Newtonsoft.Json.Serialization.JsonObjectContract contract, Newtonsoft.Json.Serialization.JsonProperty containerProperty, Newtonsoft.Json.JsonReader reader, System.Type objectType) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:2177) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObjectUsingCreatorWithParameters (Newtonsoft.Json.JsonReader reader, Newtonsoft.Json.Serialization.JsonObjectContract contract, Newtonsoft.Json.Serialization.JsonProperty containerProperty, Newtonsoft.Json.Serialization.ObjectConstructor`1 creator, System.String id) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:1920) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateNewObject (Newtonsoft.Json.JsonReader reader, Newtonsoft.Json.Serialization.JsonObjectContract objectContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, Newtonsoft.Json.Serialization.JsonProperty containerProperty, System.String id, System.Boolean& createdFromNonDefaultCreator) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:2296) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject (Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, System.Object existingValue) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:488) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal (Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, System.Object existingValue) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:293) Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize (Newtonsoft.Json.JsonReader reader, System.Type objectType, Boolean checkAdditionalContent) (at C:/Project/Github/Json.Net.Unity3D/src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs:167)