I've got two instances of subtitles failing (Quest 3):
Both occur when there is a local funscript And the .srt both present in the Quest 3's local Interactive folder.
In both cases the steps for this to fail are:
Wait for the funscript to load
Toggle subtitles to enabled
Browse to the local Interactive folder
Select the correct .srt
Wait for the funscript to load once more.
In neither instance, does the .srt actually load. Different results depending on how though:
For an SLR streamed video, after attempting to load the .srt, subtitle setting states 'Auto generated en'
For a DLNA video, after attempting to load the .srt, subtitle setting states 'None'