When a reprojected map is requested and viewed, some of the features no longer display. This is particularly noticeable when a browser is resized.
When data is reprojected, additional points often need to be added for the calculations.
Include the FILTERDENSIFY tag in the map configuration file along with FILTERCOORDSYS.
FILTERDENSIFY sets the tolerance for how many additional points are added to the filter. In some cases, features may continue to drop out on one or more layers. If so, set DENSIFY for these layers. DENSIFY adds points to the layer itself while FILTERDENSIFY adds points to the filter.