On both my Android TV (Sony 2015) and my Fire Stick subtitles in the ASS format don't show up when enabled with the synology server beta (both .net and mono).
The subtitles show up on latest stable release. Every other format of subtitle file I tried works fine (VTT, SRT, PGS, VOB) and every other client I tried works fine.
Logs: sendlogs_david-nas_synology_apollolake_218+_20181206T171614UTC.tgz