I have defined three regions, `Slice1`

, `Slice2`

and `Slice3`

.

```
Slice1 =
Polygon({{0, 0}, {1, 0}, {1, 1/(Sqrt(3))}, {1/2, Sqrt(3)/2}});
Slice2 =
Polygon({{0, 0}, {-1, 0}, {-1, 1/(Sqrt(3))}, {-1/2, Sqrt(3)/2}});
Slice3 =
Polygon({{0,
0}, {-1/2, -Sqrt(3)/2}, {0, -2/Sqrt(3)}, {1/2, -Sqrt(3)/2}});
CombinedSlice = RegionUnion(Slice1, Slice2, Slice3);
RegionPlot(CombinedSlice, AspectRatio -> Automatic)
```

When I `RegionPlot`

the combined plot, `Slice3`

does not have correct boundaries. The boundary shows up correctly when I plot `Slice3`

individually.

I am using Mathematica 12.0