Fixing AOT errors in iOS with BinaryWriter

I have a mobile Android game on the market, and I'm trying to port it to iOS. I have the game running on my test device, but I'm getting the following AOT exception when I try to save game progress:

 EXCEPTION: SaveState - Attempting to JIT compile method 'System.Collections.Generic.Dictionary`2<string, object>:Do_CopyTo<System.Collections.Generic.KeyValuePair`2<string, object>, System.Collections.Generic.KeyValuePair`2<string, object>> (System.Collections.Generic.KeyValuePair`2<string, object>[],int,System.Collections.Generic.Dictionary`2/Transform`1<string, object, System.Collections.Generic.KeyValuePair`2<string, object>>)' while running with --aot-only.
   at System.Collections.Generic.Dictionary`2[System.String,System.Object].CopyTo (System.Collections.Generic.KeyValuePair`2[] array, Int32 index) [0x00000] in <filename unknown>:0 
   at System.Collections.Generic.Dictionary`2[System.String,System.Object].GetObjectData (System.Runtime.Serialization.SerializationInfo info, StreamingContext context) [0x00000] in <filename unknown>:0 
   at System.Runtime.Serialization.Formatters.Binary.ObjectWriter.GetObjectData (System.Object obj, System.Runtime.Serialization.Formatters.Binary.TypeMetadata& metadata, System.Object& data) [0x00000] in <filename unknown>:0 
   at System.Runtime.Serialization.Formatters.Binary.ObjectWriter.WriteObject (System.IO.BinaryWriter writer, Int64 id, System.Object obj) [0x00000] in <filename unknown>:0 
   at System.Runtime.Serialization.Formatters.Binary.ObjectWriter.WriteObjectInstance (System.IO.BinaryWriter writer, System.Object obj, Boolean isValueObject) [0x00000] in <filename unknown>:0 
   at System.Runtime.Serialization.Formatters.Binary.ObjectWriter.WriteQueuedObjects (System.IO.BinaryWriter writer) [0x00000] in <filename unknown>:0 
   at System.Runtime.Serialization.Formatters.Binary.ObjectWriter.WriteObjectGraph (System.IO.BinaryWriter writer, System.Object obj, System.Runtime.Remoting.Messaging.Header[] headers) [0x00000] in <filename unknown>:0 
   at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize (System.IO.Stream serializationStream, System.Object graph, System.Runtime.Remoting.Messaging.Header[] headers) [0x00000] in <filename unknown>:0 
   at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize (System.IO.Stream serializationStream, System.Object graph) [0x00000] in <filename unknown>:0 
   at EncryptionManager.EncryptFile (System.String _path, System.Object _data, System.Byte[] _key) [0x00000] in <filename unknown>:0 
   at StateManager.SaveState () [0x00000] in <filename unknown>:0

I understand the issue, and I've tried creating AOT hints for the compiler with no luck. Can anyone suggest a fix? I don't want to incorporate another library or package because I want to keep the Android and iOS code base the same, and I already have Android users with save data. Here is my current setup:

     public static void EncryptFile(string _path, object _data, byte[] _key = null)
     {
         // Check parameters
         if (_data == null) return;
         if (_path == null || _path.Length <= 0) return;
 
         // Create AES service provider
         using (RijndaelManaged aes = new RijndaelManaged())
         {
             // Set aes paramaters
             aes.Mode = CipherMode.CBC;
             aes.Padding = PaddingMode.ISO10126;
 
             // Set key
             aes.Key = _key;
 
             // Set iv
             aes.GenerateIV();
 
             // Create file stream
             using (FileStream file = new FileStream(_path, FileMode.Create))
             {
                 // Write iv to file
                 file.Write(aes.IV, 0, aes.IV.Length);
 
                 // Create crypto stream
                 using (CryptoStream crypto = new CryptoStream(file, aes.CreateEncryptor(aes.Key, aes.IV), CryptoStreamMode.Write))
                 {
                     // Serialize data
                     BinaryFormatter bin = new BinaryFormatter();
                     bin.Serialize(crypto, _data);
                 }
             }
         }
     }

I'm passing in a Dictionary< string, object > for _data.