My husband and I love Larian too much to ask for a refund, we will wait and hope they will fix this. It should be fixable - after all, DOS 2 worked perfectly in split screen, this is basically the same type of game mechanics-wise, but with beefier graphics.
For one, they should disable the Quality mode for the split screen and just go with Performance. I mean, we've initially selected Performance in the first place, but apparently the game defaults to Quality immediately when you enter split screen (which is ridiculous). And since the game freezes more frequently as you progress, this insinuates some kind of memory leak, unoptimized scripting or stacking conditions (I'm comparing these problems to Skyrim, but it may not be the same thing).
Whatever it is, I still have faith in them. They have provided unprecedented experience and entertainment for us in the past, we have a friggin' Platinum trophy in DOS 2 on PS4.