Using publicly available data sets and reports on social media and in the press, the organization pinpointed incidences of "GPS spoofing" when an electronic weapon scrambles the data stream between nearby ships, vehicles and aircraft and the satellites that help power their navigation systems. In many cases, like one incident that occurred near the Kerch Strait, the site of a skirmish late last year between Ukrainian and Russian forces. As Putin and a convoy of construction vehicles crossed a new bridge over the Strait, the GPS of ships docked in a nearby harbor suddenly went "haywire."
Here's more on that from CBS News:
The ships' GPS systems suddenly began to indicate they were actually 65 kilometers away, on land, in the middle of an airport.