The content type text/xml; charset="utf-8" of the response message does not match the content type of the binding (text/xml; charset=utf-8)

It would indeed seem that the .NET Core version is more picky about this. In any case, I managed to solve it using a Custom Encoder.

I blatently stole the CustomTextMessageEncoder from Github. I added the following method:

public override bool IsContentTypeSupported(string contentType)
{
    return true;
}

And stole CustomTextMessageBindingElement and CustomTextMessageEncoderFactory from the same place.

I added them by creating a custom binding (basicBinding is the binding I had before):

var customBindingElement = new CustomTextMessageBindingElement("UTF-8", "text/xml", MessageVersion.Soap11);
var binding = new CustomBinding(basicBinding);
binding.Elements.RemoveAt(0);
binding.Elements.Insert(0, customBindingElement);
var client = (T2)Activator.CreateInstance(typeof(T), binding, address);

I use Activator as I generate my proxies dynamically. Just replace with a call to the WCF generated client.

Quite a lot of work for two misplaced quotes :D