“But the PLAN operates in the same area and they *don’t* run into merchant shipping.”
Our Navy has a lot of manning issues, no doubt. But the fact that we suddenly can’t rely on our satellite-base NAV systems in THAT part of the world suggests localized jamming. Especially when you realize that there are no reported close-calls with PLAN vessels.
The jamming *post-dates* the incidents where the US Navy rammed merchant vessels and is (IIRC) currently confined to the Hong Kong vicinity, not anywhere near the incidents in question. It also doesn’t explain why people weren’t looking out the windows to see what’s there - GPS doesn’t tell you where *other* ships and vehicles are.
Further, one reason the PLAN isn’t having problems despite what is presumably their own jamming is that their vessels do not use the US GPS system, or at least do not rely on it entirely. Which makes sense as the US GPS is under US control and subject to being turned off if the US wishes it. Which is why there’s the Russian GLONASS system, the European Galileo system... and of course, the Chinese have their own BeiDou Navigation Satellite System.