It's unfortunate that Roku is unable to fix this issue. I'm not necessarily a huge fan of Amazon, and really dislike their interface. However, I do watch a lot of anime with my daughter, and a lot has subtitles. Trying to watch where the video is zoomed in and you can't see the subtitles any longer is beyond frustrating.
At this point, I will be abandoning Roku and buying firestick devices. At least they stream the content consistently. Such a shame. I've been a fan of Roku for years.