Why does one Plex client (web) show correct subs and another client (firestick) wont?

Plex Players
1

I am watching a TV episode (from Plex Server 1.24.5.5173) and if I choose English subs from opensubtitles.org it shows fine on web client. But then if I watch the same episode (even if I choose to resume) on Plex client on an amazon firestick, the subs all come up as Arabic. Whatever I choose on that client forces arabic subs even though when I use the web client its fine.
Is there a setting somewhere that means the client can override what I set in the Plex server?

Any pointers appreciated.

2

Ah ok - so in the firestick Plex options I went into the option to change subtitles from “Automatic” to “Always” and it now works. But why?