GPS unavailability is not uncommon
That's why my RV has VOR/ILS and a VFR GPS.
I've had my GPS show zero groundspeed and no progress on the moving map on at least two occasions for 20 minutes or so. My phone, which was down between the seats, indicated normally. I theorize that the phone was shielded from the jamming/spoofing by the airframe, but still had a good GPS signal.
Here's the current GPS notams for my airport:
Navigation NOTAMs
!GPS 03/087 KZLC Navigation Global Positioning System (WSMRNM Global Positioning System 21-07) (including Wide Area Augmentation System, ground-based augmentation system, and ADS-B) May not be available WI A 359 nautical miles radius centered at 333706N1063053W (TCS049043) flight level 400-unlimited, 312 nautical miles radius at flight level 250, 222 nautical miles radius at 10,000 feet, 220 nautical miles radius at 4,000 feet above ground level, 164 nautical miles radius at 50 feet above ground level. Daily 0600-1400 Mar 30, 2021 0600Z to Apr 2, 2021 1400Z
!GPS 03/079 KZLC Navigation Global Positioning System (WSMRNM Global Positioning System 21-22) (including Wide Area Augmentation System, ground-based augmentation system, and ADS-B) May not be available WI A 352 nautical miles radius centered at 332953N1063527W (TCS056037) flight level 400-unlimited, 296 nautical miles radius at flight level 250, 233 nautical miles radius at 10,000 feet, 232 nautical miles radius at 4,000 feet above ground level, 161 nautical miles radius at 50 feet above ground level daily 1830-2230 Mar 26, 2021 1830Z to Apr 6, 2021 2230Z
!GPS 11/021 GPS Navigation PRN 11 unserviceable Nov 10, 2020 1500Z to Apr 7, 2021 1500Z