And a comment from a Scott H. on the same site:
The airline I work for is having this issue. The story we’re getting is that at approximately 3:00z on 6/9/19, the WAAS system on all of the GPS satellites received a software upgrade and that the software upload was somehow corrupted. This means that aircraft equipped with the WAAS MMR’s (Multi mode receivers) manufactured by Rockwell Collins are unable to resolve the WAAS signal from the satellites, thus causing MMR and GPS failure messages in the aircraft. The aircraft equipped with the pre WAAS MMR’s are not affected. Our airline is working with Rockwell Collins, the aircraft manufacturer and the FAA to receive permission to return our aircraft back to the pre WAAS configuration until the WAAS systems on the satellite constellation are operating normally again.