SOLVED-Unexpected event 20 playing MP3 with SDK videoplayer

Hi all,
I'm trying to get mp3 audio to play alongside of my live hls video, so I followed the helpful advice from Belltown here: viewtopic.php?f=34&t=51192
However, when I go to play an item, the display breifly flashes it's "retrieving" and then falls back to the previous screen.

The relevant debug output says:

showHomeScreen | msg = Stream started. | index =  0
Unexpected event type:  20
showHomeScreen | msg = Content contains no playable tracks. | index =  0
Video status:  0  0
showHomeScreen | msg =  | index = -5
Video request failure: -5  1

I'm trying to use 120MB mp3s that are about an hour long and have id3 tags, however, in these forums there seems to be a question about what is supported, so I also tried short, small mp3s without metadata of any kind, CBR 128kb/s and 32,24, and 16 bit at 48kHz and also 44.1kHz - all to no avail - same error. I've tried non-existent files (which produces an obvious error) and checked the server logs, so I know the files are being pulled by the roku. But now I'm at a loss! Any help would be fantastically helpful 🙂

My test Roku: Model: 3100X, Software version: 4.9 - build 5060

Thanks so much!