The Android client has had VOBSUB issues for a long, long, time and have never been addressed.
https://forums.plex.tv/t/mis-rendered-vobsubs-an-issue-since-2017/
https://forums.plex.tv/t/nvidia-shield-tv-mis-rendered-vobsubs-mkv-mpeg2/
https://forums.plex.tv/t/some-subtitles-missing-via-direct-play/
Don’t expect anything to be fixed. The last time VOBSUBs seemed to work 100% in Android was 6.13.7…which was Feb 2018
