Textastic has a syntax definition for R.

Yes, I have seen this happen on my machine, too. I'm not sure why it happens yet. I'll need to investigate, but it's not easy to debug.

I just tried to reproduce this: if I enable "Smart Punctuation", I see the behavior you are seeing when using an external keyboard. If I disable "Smart Punctuation", I get regular quotation marks.

I've attached a screenshot of the setting that needs to be disabled:

Do you have "Smart Punctuation" disabled in Textastic's settings?

Are you on iOS 13? I'm asking because there is a bug in iOS 13 so that touch scrolling does not work.