A random sequence in an innocuous GPS message field is likely encrypted traffic from the U.S. military’s system for remotely updating cryptographic keys around the world.
If the OTA distribution system went online in 2011, it would have been for P/Y code, which is the original military-use code that launched with the GPS satellites.
P/Y originally provided better position precision than the unclassified C/A code, under a program called Selective Availability (SA). SA was deactivated in 2000 by executive order of President Bill Clinton. Since that time, P/Y only provides an anti-spoofing feature that helps receivers to authenticate genuine GPS.
The military is now in the process of moving to a new, third code called M-code. M-code required updated satellites to be launched, as old ones were retired, and it required big overhauls to the ground control networks. After about 10 years of delays, M-code is now in process of rolling out to end users in the military.
I’m conclusion, a possible reason to retire this old program is because users are now moving to M-code.