Yep, two or three times over the last few years, north eastern med or over eastern Turkey..and it happened to several of my colleagues as well.
The symptoms I saw weren't quite as dramatic as those seen by magplug, If I remember correctly the first clue (Boeing) was usually the ND displaying "inertial", then several seconds/minute or so later the "Unable RNP" msg coming up..and all resolved quite simply by ensuring DME/DME updating was available...
Not a big deal if going back to north west europe because you'd usually get valid GPS updating back once you were out of the area but if you were going the other way and it happened shortly before descent into one of the nearby airports who were offering RNP approaches it meant a quick replan/rebrief.
Last edited by wiggy; 1st Nov 2020 at 17:50.