Also, I don't want to freak folks out but I've gone to extremes to figure this out so far.
I've another test where I've taken the Steam version and made a hybrid to non-Steam via using the non-Steam cheevo code and options code. So, this is exactly Steam but the VN thinking it's non-Steam (even using the non-Steam persistent and save system folder structure). It still borks.
It is starting to look like it's save file related. Again, not trying to freak folks out but if it is save file related this... is not a good sign. All these old saves work just dandy pre v0.8 so I'm currently left with what's different and that is the migration of v0.8 to RenPy 8 and it's handling of the previous save file structure. I sincerely hope this isn't the case... but the hybrid build above is pointing to exactly that.
Damn it.... I'll start pulling apart save files I guess. This has been a massive delay on me getting the mod updated of the new content but I have to sort this if only for my own peace of mind. It's imperative.