Marc,
Perhaps your NanoVNA calibration is bad. If you leave the NanoVNA connector open does it show an extremely high SWR, as it should? If you place the calibration load on the NanoVNA connector does it show 1.0:1 VSWR, as it should?
Another possibility is that your feedline has become very lossy. A feedline with 10 dB loss would produce results similar to what you are seeing.
Jon w2anz
Jon MacGahan