Exact same issue.
MSI 970 4gb
i5 4690k
16 gb memory
The game runs like a dream in singleplayer at ultra everything 60 fps triple buffer blah blah blah, it only crashed when split screen is enabled. (It also crashes if I put everything at low, and 30fps)
This has been an issue from launch for me and I've spent hours trying to test it and "make it crash," and it seems completely inconsistent. It has definitely gotten worse with patch #3, before that, it would crash a few times at the beginning, then start working fine, almost like an old car warming up, now I can't get it to load in and run for more than 60 seconds most of time time, other times it'll run for 5 minutes then crash.
Happens in act 1, I haven't even gotten to act 2.
Fingers crossed, when they push out the cosplay patch it will resolve co-op issues and split screen, but any sort of communication from larian would be great that they're even aware of this issue.