[bornagainpenguin]

So I was fiddling about with things again later and I think I've identified what is going on but not at all certain what to do about the issue (aside from embarking upon a replacement of all my files of this type, that is) apparently the issue I'm having is more or less entirely restricted to my anime collection, which as much as possible I select for dual audio.  Unfortunately the default choices made by fansubbers seems to be to give a dual audio option but if you choose English then they only subtitle signs and other onscreen text and maybe the theme song.  I've played with settings in Kodi but for whatever reason I cannot seem to lock in the preferences to give me English audio and Japanese subtitles without it affecting other stuff.

Outside this incredibly niche situation the subtitles have been consistently working for me.  So I apologize for wasting your time on this, but I wanted to at least let you know what was going on.