The GPS unit needs to figure out the locations of all the satellites before it can use them to figure out your positions. The satellite positions are expressed as a function of time, and the times used are measured in seconds within the current GPS week[1].

This is the mechanism that I'd expect someone messed up. I'd expect location errors more than time errors, but because you can get time out of GPS then someone probably has.

[1] https://gssc.esa.int/navipedia/index.php/GPS_and_Galileo_Sat...