I had same issue as well, was doing a mission first day was fine, then next day I try to continue periodic lags spikes then eventually this UE4 memory crash.
In order to save your character go here: "C:\Users<YOURNAME>\AppData\Local\Icarus\Saved\PlayerData<RANDOM_NUMBER\Prospects" rename the first file to corrupted and then rename the next file down by removing the backup after the .json and load in.
Now this is only a temperary fix to get in and save your character. Every lag spike increases that save files memory which will in time lead to that UE4 crash. So I recommend get in and get your workshop gear and head to the dropship to leave.