Roku stalls at 33% on H.264 + 5.1 AAC (HLS audio transcode), regression

Roku app stalls at 33% on H.264 + 5.1 AAC when the video is sent as-is and the audio is converted to AC3 over HLS. This is a regression (the same files used to play). Setup Plex Media Server 1.43.1.10611 on Linux (Ubuntu) Client: Plex for Roku (Software Version 16.0) Roku audio settings are all Auto, outputting to a Sonos Arc over HDMI ARC.