Update for HF has been with giants for almost 2 weeks now.
From what I've been seeing is if you use any shader mods, they are breaking game saves since the release of the DLC. I've had no comments saying its my mod causing the issue.
Only way to figure out which one is causing it, is to load 10-15 or so mods at a time until you find the one that is causing the issue. But if youre on PC I would start with any script mods. Those usually break things first.