"So while it's definitely an issue, isolating and reproducing it seems to be incredibly difficult."
Alright Thandal, I have a challenge for you then over the next few weeks if you so choose to undertake it. Delete the 'Default.sfar' file under the directory specified below.
C:\Program Files\Origin Games\Mass Effect 3\BIOGame\DLC\DLC_EXP_Pack001 or wherever you have ME3 installed.
Then delete the 'installerdata' file in the directory
C:\Program Files\Origin Games\Mass Effect 3\BIOGame\DLC\__metadata\DLCEXPPACK001\__Installer or again if you have ME3 installed somewhere else use that path.
Then, it is as simple as hitting the repair button on the DLC. It should automatically reinstall it. From there you can get to the point where we are having the freezing issue in probably 2-4 hours on the easiest difficulty. If you don't encounter the same crash, then we can say that it probably isn't a corrupted file being sent out from Origins.
This challege would apply to anyone else that hasn't had the issue and is looking at this thread as well. Now, I completely understand if you don't want to do this challenge. If my game was working I certainly wouldn't want to do anything to **** it up. But there seem to be a few issues with Leviathan not just related to this specific problem (http://answers.ea.com/t5/Mass-Effect-3/Mass-Effect-3-Leviathan-DLC-Glitch/m-p/2440121#U2440121). I could certainly be wrong, but I believe there is something wrong with the file EA is sending out or perhaps the installation process itself is somehow corrupting the file. I don't know, I'm not technical with coding and the like, but considering how different everyone's hardware seems to be that is getting this glitch I don't think this is a hardware issue.