Recently been working in a UE4 project where a very similar sounding D3D12 crash was happening to me whenever I messed around with water bodies in a complex map. Call me crazy, call this out there, but I narrowed my problem down to something to do with Steam.
If Steam was running, consistent crash every time at the same point. If Steam was closed, no crash. I have no idea why but that was what solved it for me when nothing else would work. Lost a couple of days over it until I finally tried that. Not saying it will work for anyone else reading this but if all else has failed, there’s one more thing you can try.
I truly know the frustration and clumps of hair torn out over this stuff.