Playback Issues - Plex App vs Web Browser + Mobile

Server Version#: 1.42.0.9975
Player Version#: 1.109.0.329-ea562b95

I’m having issues with playback of some content (TV and films). All of the media files are located in the same location on a Synology NAS.

The issue is always on the Plex App on the PC. Typically, after selecting play, it just sits there and nothing plays, even though it does appear to buffer (seen by the light orange bar). If I use a web browser to access Plex, that works fine. If I use the mobile Plex App (Android), that also works.

This suggests to me an issue with codecs, however my understanding is that the Plex PC App has better overall compatibility than what a web browser typically provides.

Overall, the Plex PC App works with 95% of the content I play, it’s just the 5% that doesn’t and yet it always does then on the same PC but in a browser and the mobile Plex app.

Additionally, if I use VLC on the same PC, it works 100% of the time.