[=Kenomica;232192]
I’m using baked lighting, so I will definitely give it a go. Thanks for the tip.
That did it! THANK YOU!
EDIT : Though it is VERY unstable. After building lighting, there is till a 50/50 of a hard crash whenever I open a map or compile a blueprint.
Also, rotated landscapes still have terrible splotches everywhere, despite the patch note stating it was fixed. Back to 4.6 for me.
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I’m afraid you’re right 
If I restore static lighting to the project it immediately re-exhibits the crash-while-opening syndrome again. So means my workaround just allows us to salvage a 4.6 project by opening it without lightmass.
I’m now trying to tweak as many static lighting related settings/map actors as I can to deduce the root cause, will post any news of success. Might just have to submit a project to Epic on the answer hub as there’s no useful info in the crash either apart from the notorious Access violation writing location <>
UPDATE:
Believe I’ve narrowed it down: Loading crashes for my map if any blueprints in it contain an Instanced Static Mesh component to which instances are added right from the BP’s Construction Script (eg: think static procedural foliage decorations around your actor that you might have created in the construction script for ease of creation or for applying specific visual patterns/etc).
For whatever reason, if you use static lighting and have any such actors in your map then the editor crashes while trying to load that map if its lighting has already been built. The workaround I’m currently testing is to generate all such foliage through a proxy object or a blutility so you don’t have to rely on construction scripts for populating any “static” instanced meshes.
FWIW, used to work in 4.6.1, 4.5, etc without issues.