In all these cases, of course, GPS has not actually failed. It was still working fine. However, local interference is a factor, and that is almost certainly what occurred in these cases. There is a huge difference between an IFR certificated (TSO'd) unit, and a handheld unit. As the frequency spectrum becomes evermore crowded, particularly in Europe, things may get worse. Let's hope Galileo manages to squeeze in somehow, and relieve the situation - though you will have to pay for it, of course.