The mesa issue is absolutely not related to the subtitle issue.
After identifying that it was the changes introduced when adding the front-to-back rendering option (while still in back-to-front rendering no less) that was the source of the subtitle breakage, I tried reverting those changes on top of the current Kodi used by LibreElec. While it is a big patch file, I do have a system that is current and does have subtitles.
chewitt I'm fairly certain this is a patch that would never be accepted in LibreElec, is there any thoughts on who might be able to identify where the back-to-front GLES rendering messes up subtitles? I'm not sure sarbes is around, however I did leave a comment on the merged Kodi pull #22919 about the breakage.