I had the same issue with Microsoft cumulative update KB4524149 (dated October 4th). Illustrator 2018 would open, but would crash upon trying to open any files. I could open files in safe mode, but not in a clean boot. My tech knowledge isn't enough to know why the update conflicts with Illustrator, but eventually I uninstalled the update and Illustrator works fine again.
I had the same issue with Microsoft cumulative update KB4524149 (dated October 4th). Illustrator 2018 would open, but would crash upon trying to open any files. I could open files in safe mode, but not in a clean boot. My tech knowledge isn't enough to know why the update conflicts with Illustrator, but eventually I uninstalled the update and Illustrator works fine again.