This question is related to RegionPlot not plotting some regions.
I have the following region and want to plot the area and the boundary. In Mathematica 10.3.1 it works fine but not in 10.4.
reg = RegionDifference[Disk[{2, 0}, 2, {0, \[Pi]}],Disk[{1, 0}, 1, {0, \[Pi]}]];
{RegionPlot[reg, AspectRatio -> 1/2, ImageSize -> 250],
RegionPlot[RegionBoundary@reg, AspectRatio -> 1/2, ImageSize -> 250]}
How can one get rid of this behavior?