Probably because you have an error in your program. Or in your SVG file. Since we have neither, we can only play guesses...
I also see that Texas (I recognize it because of the Texas Instruments logo...) has a strange line across it. And perhaps around the Great Lakes. Again, not knowing how you display the SVG, I don't know why they are there.
Thank you for your response. Because I couldn't figure this problem out previously, I wrote code to display the states with different colors (not in a buffer) and then just drew the full map over them. This seems to work fine, but do you know if there is any reason that drawing in a buffer would be better than drawing them under the other map?
No, because as I wrote, I cannot reproduce your problem. Drawing on the screen is actually drawing on the main PGraphics of the sketch, so these operations should be similar, or identical. Unless you use a different PGraphics, like JAVA2D for one, P2D for the other.