Subtitles won't play

Hi All
I'm sure this has been asked, but I haven't found a solution as yet.
I have a dedicated Debian Stretch headless server running on a dissused laptop. The laptop is an i5 quad core @ 2600Mhz and has 8Gb ram. So it should be plenty to do what I require.
On to the problem:
If I add subtitles (srt) to any movie (mkv) it will not play at all on any DLNA client. It does however play on my laptop with subtitles when managing PMS. The subtitle files are in the same folder as the movie and have the same name as the movie.
If I remove the association of subtitles within PMS the movie plays on the DLNA client as expected but obviously without subtitles.
As the movies play on my laptop I am guessing this is probably a DLNA issue of some description. But I'm not sure what to look for.
I've attached the profile for one of the clients.
All clients are within my LAN.
Regards
Fred
Answers
I have a similar problem. Could you solve the problem?
TV's: Hisense H43M3000 (4K) & Hisense H32M2600
Home theater: Yamaha V373
Server: OEM NAS Intel J1900, 4GB RAM, 14 SATA PORTS, 2x TOSHIBA 2TB, 2x Seagate 4TB 2,5". Total power consumption: 40W
LAN: 1000M Ethernet , Cat6 wired.
PC's: Lenovo X230 (i7 +16GB RAM + msata SSD+ 500GB SHDD+Docking station+22" IPS monitor) + HP Elitebook 2170p
Hello
No I did not resolve this issue. I have resorted to ripping my movies with the subtitles contained within the file. Hence no transcoding occures.
Regards
Fred
A similar question was asked and answered here.. It may help you as well.
https://forums.plex.tv/discussion/255111/dlna-and-subtitles