SOLVED: Playback Issue for some Media

[m61x]

Okay, everyone, I feel a bit silly right now. After a week of debugging, I finally posted about the issue, only to figure it out just 12 minutes later! Turns out Jellyfin (or maybe the browser) doesn't seem to like the mp42 codec ID. Once I converted everything to isom, it worked perfectly.

I'll leave this post up in case anyone else runs into the same issue. Sorry for the confusion!