AC68U upnp/dlna server, external subtitles not displaying

Hi,

I have an HDD connected to my router. I enabled the upnp server and everything works except the external subtitles.

I tried playing on my laptop/ps4/tv dlna/Android phone, nothing works. Embedded subtitles display just fine but external don't. I have them named the same as the video file in the same directory but it doesn't help.

My router is running Merlin FW 380.65_4.

Any ideas? Thanks!