i'm having the exact same issue, using a NVIDIA GeForce GTX 650
enb version 307, latest 1.6.3 version of fallout 4
this problem ONLY happens for me when i have it set to UsePatchSpeedhackWithoutGraphics=true
this is my current settings
http://i.imgur.com/OSHkFpA.png you already have a save at the exact spot i'm encountering it myself
i have been tweaking my settings to see if i can fix it on my end, but so far it hasn't worked
EDIT: even with full ultra settings it's still doing it, nothing short of uninstalling ENB causes it to stop