The image was screen-capped from a previous attempt and the attached log was grabbed right after a subsequent attempt, so it should have the relevant data.
Regardless, I deleted the Plex app from my phone, re-installed, and was able to download a different movie, but when I tried to download the same movie as previous attempts, I got the same error, and then it tried to download again without my prompting.
And this is probably not necessary, but here is a screen video of the download attempt (to scrub through, not exactly a really a riveting watch): Dropbox - PlexDownload.mp4 - Simplify your life