Just heard back from Roku support. Sounds like they do consider it a bug, but it won't be fixed until July at the earliest. He did suggest a workaround though. Apparently JSON feeds don't trigger the bug like RSS feeds do, since you can specify the sorting in the JSON feed.
Here's the response I received:
At this time, we have an open bug report on the issue you reported regarding categories not displaying in chronological order. We will continue to track the bug, but at this time it is uncertain when it will be resolved.
Thankfully, your content will continue to display within your channel, albeit out of order. If you were to convert your feed to the JSON feed format, then you could configure a "playlist" within your feed. Essentially, a playlist acts as any other category in your channel, but it allows the publisher to control the order that the content appears in. This is one potential solution for you to fix the display of your category.
If you do not convert to JSON, then I suggest that you check-in with us again early next quarter to see if there have been updates on this ticket.
Guess I better get started on building the JSON feed! 😕