This is working now. No code changes required.

@Samwilson. On this document, my cursor was on the text Russia Russia where I added additional text. After reload the document focus was still at the top of the document per screen shot below
Article link: https://en.wikipedia.beta.wmflabs.org/wiki/Conflict-title-0.0009906783829625176-Iñtërnâtiônàlizætiøn?action=edit&veswitched=1

I think that's the correct behaviour. T294977 is about making the preview pane automatically scroll to match the current editing position (which I think is what you're expecting there?).

This ticket is about making sure that the preview pane says wherever it currently is scrolled to (i.e. "where I was last viewing the page").

At least, that's how I'm reading it. I might be wrong!

In some early iterations of RPT, I think we had the preview pane jumping to the top on every preview reload, which is why this bug was raised.

Discussed this change with product and it works as expected. Thanks for taking a look at this Sam.