iOS Possible memory leak when large TextAsset is loaded

I have a large xml file which is loaded from a TextAsset in an asset bundle, once loaded I parse the elements and use the data contained to create a database of objects with various features and parameters.

My problem here is that on iOS there is a surprisingly large memory spike when I assign the TextAsset.text to a string, or read it using a string reader. I can manage all memory increases due to the bundle itself, by unloading the bundle, unloading unused assets and destroying the text asset. but nothing I do seems to get rid of the increase created by assigning the TextAsset.Text to a string. I've added the code snippet I'm testing below.

This part works just fine, the memory used by loading the bundle request and the Text asset is released when I destroy the textasset and unload unused assets

 if (bundle.mainAsset != null)
             {
                 AssetBundleRequest request = bundle.LoadAssetAsync("data", typeof(TextAsset));

                 yield return request;
 
                 TextAsset xmlFile = request.asset as TextAsset;

The Parser.Xml is a string, I've also tried directly loading it to an XMLDoc, and using a stringReader, once it loads the text into the string, the memory goes up and will not go down no matter what I do after

                 parser.Xml = xmlFile.text;

This is more or less everything I could think of to release the memory

                 parser.Xml = null;
                 DestroyImmediate(xmlFile,true);
                 System.GC.Collect();
                 request = null;
                 bundle.Unload(true);
                 Resources.UnloadUnusedAssets();

    }

I've tried everything I could think of to get it to release the memory, not sure if its a memory leak or if I'm missing something here, I only have this issue on iOS device (profiled using instruments). Don't see any evidence of it when I profile memory in editor