I encountered the same error using Google.Protobuf, building an Android package runtime with IL2Cpp
error:
ExecutionEngineException: Attempting to call method ‘Google.Protobuf.Reflection.ReflectionUtil+ExtensionReflectionHelper`2[[Google.Protobuf.Reflection.FieldOptions, Assembly-CSharp, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null],[Google.Api.FieldBehavior, Assembly-CSharp, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null]]::.ctor’ for which no ahead of time (AOT) code was generated.
System.Reflection.RuntimeConstructorInfo.InternalInvoke (System.Object obj, System.Object parameters, System.Boolean wrapExceptions) (at <00000000000000000000000000000000>:0)
System.RuntimeType.CreateInstanceImpl (System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object args, System.Globalization.CultureInfo culture, System.Object activationAttributes, System.Threading.StackCrawlMark& stackMark) (at <00000000000000000000000000000000>:0)
System.Activator.CreateInstance (System.Type type, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object args, System.Globalization.CultureInfo culture, System.Object activationAttributes) (at <00000000000000000000000000000000>:0)
Google.Protobuf.Reflection.ReflectionUtil.CreateExtensionHelper (Google.Protobuf.Extension extension) (at <00000000000000000000000000000000>:0)
Google.Protobuf.Reflection.ExtensionAccessor..ctor (Google.Protobuf.Reflection.FieldDescriptor descriptor) (at <00000000000000000000000000000000>:0)
Google.Protobuf.Reflection.FieldDescriptor.CreateAccessor () (at <00000000000000000000000000000000>:0)
Google.Protobuf.Reflection.FieldDescriptor.CrossLink () (at <00000000000000000000000000000000>:0)
Google.Protobuf.Reflection.ExtensionCollection.CrossLink () (at <00000000000000000000000000000000>:0)
Google.Protobuf.Reflection.FileDescriptor.BuildFrom (Google.Protobuf.ByteString descriptorData, Google.Protobuf.Reflection.FileDescriptorProto proto, Google.Protobuf.Reflection.FileDescriptor dependencies, System.Boolean allowUnknownDependencies, Google.Protobuf.Reflection.GeneratedClrTypeInfo generatedCodeInfo) (at <00000000000000000000000000000000>:0)
Google.Protobuf.Reflection.FileDescriptor.FromGeneratedCode (System.Byte descriptorData, Google.Protobuf.Reflection.FileDescriptor dependencies, Google.Protobuf.Reflection.GeneratedClrTypeInfo generatedCodeInfo) (at <00000000000000000000000000000000>:0)
Google.Api.FieldBehaviorReflection..cctor () (at <00000000000000000000000000000000>:0)
User.V1.StoryReflection..cctor () (at <00000000000000000000000000000000>:0)
User.V1.ChapterReflection..cctor () (at <00000000000000000000000000000000>:0)
User.V1.GetDataResp.get_Descriptor () (at <00000000000000000000000000000000>:0)
Google.Protobuf.JsonParser.Merge (Google.Protobuf.IMessage message, Google.Protobuf.JsonTokenizer tokenizer) (at <00000000000000000000000000000000>:0)
Google.Protobuf.JsonParser.Merge (Google.Protobuf.IMessage message, System.IO.TextReader jsonReader) (at <00000000000000000000000000000000>:0)
Google.Protobuf.JsonParser.Parse[T] (System.IO.TextReader jsonReader) (at <00000000000000000000000000000000>:0)
WebReqMgr+<>c__DisplayClass5_0.b__0 (Newtonsoft.Json.Linq.JObject json) (at <00000000000000000000000000000000>:0)
WebReqMgr+d__22.MoveNext () (at <00000000000000000000000000000000>:0)
UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) (at <00000000000000000000000000000000>:0)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.RuntimeConstructorInfo.InternalInvoke (System.Object obj, System.Object parameters, System.Boolean wrapExceptions) (at <00000000000000000000000000000000>:0)
System.RuntimeType.CreateInstanceImpl (System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object args, System.Globalization.CultureInfo culture, System.Object activationAttributes, System.Threading.StackCrawlMark& stackMark) (at <00000000000000000000000000000000>:0)
System.Activator.CreateInstance (System.Type type, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object args, System.Globalization.CultureInfo culture, System.Object activationAttributes) (at <00000000000000000000000000000000>:0)
Google.Protobuf.Reflection.ReflectionUtil.CreateExtensionHelper (Google.Protobuf.Extension extension) (at <00000000000000000000000000000000>:0)
Google.Protobuf.Reflection.ExtensionAccessor..ctor (