“The U.S. is poised to resume shipments to Ukraine of long-range bombs known as Ground-Launched Small Diameter Bombs (GLSDB), after they were upgraded to better counter Russian jamming, two people familiar with the weapon told Reuters.”
Only took them 3 YEARS to figure out that GPS can be jammed.
The US knew that GPS could be jammed for over 20 years. That’s why newer systems like ATACMS and GMLRS (the HIMARS munitions) were made with inertial nav as well.
SDB and JDAM are older tech.
Quite what effect modern GPS jamming could have was going to be unknown until it was actually tried on a large scale.