There are "bugs" in multiple APIs handling of 180.
1. GeometryEngine.Project when converting to Web Mercator returns NaN for +/-180. It should return +/-pi*EarthWGS84Radius
2. Polyline graphics that span across the 180 line are connected the "long" way instead of the "short" way: a short line becomes one that spans the globe.
For problem 2, I understand there is a theoretical ambiguity as to which way to connect the lines. In most cases, picking the shortest path is likely to be the correct answer.