After subtitle video one of my audio track is missing
FFmpeg, by default, only picks one stream of each type (video, audio, subtitles). The user needs to set map option to select tracks for an output.
ffmpeg -i /sdcard/input.mkv -vf subtitles=/sdcard/input.ass -map 0 -c:a copy /sdcard/hrdcoded.mp4

See https://ffmpeg.org/ffmpeg.html#Stream-selection