It seems worth mentioning that the last time GPS had issues like this afaik, it was due to the US utilizing 'selective availability' due to national security issues. We used it somewhat famously during the 9/11 attacks.

Also the page 404's via archive.org, but information formerly from gps.gov can still be found here: https://archive.ph/trwOo

Edit: The selective availability page moved to https://www.gps.gov/selective-availability