This is related to your datalink weather.
The boundary of the available datalink radar data is shown by an area with diagonal stripes. In normal operation, this boundary follows the outline of CONUS if US RDR is selected, or the extent of Canadian Radar if CAN RDR is selected.
If, however, datalink radar is unavailable in a particular area for any reason, the hatched lines appear in that area. In the mountains and off the coast, hatched lines may represent no coverage below 10,000 feet. If there are radar returns in that region above FL100, the returns will be displayed as "islands of precipitation" surrounded by the hatched lines.