Yeah it coul be problem with 4gb because rvn dag reached 3.74gb. you are in windows so it can stop before rvn reaches 4gb. You can mine other coins on 4gb and rest mine. I dont have 4gb for testing.
There may be a problem with the RAM buffer overflow on the video card, but this is very easy to check if the monitor is connected to a video card with 8 GB of memory or disconnected for the test 4 GB videocards.Windows only uses the memory of the main video card that the monitor is connected to, there should be no problems with other video cards.
I recommend Hive OS. One mining farm for free.