NOAA has announced they will be shutting down their raster chart tile service on October 1st. Coastal Explorer on the iPad and iPhone uses this service for its raster chart display, so raster charts will no longer be an option on that date.
This is part of a larger project where NOAA is discontinuing production of raster and paper charts in general by 2025.
Coastal Explorer on Windows will continue to support the viewing of raster charts, but when NOAA stops producing them, the charts will no longer be available to download from within the program.