Unless you're using a very short length of coax then the coax will skew the readings. When using an antenna analyser you want to be ideally connecting it directly to the antenna feedpoint.I don't know whether my antenna was damaged in transit, it doesn't appear to have any marks on the outside, but nowhere on my antenna analyzer can i find a 50 ohm feed point moving the rings anywhere from top to bottom
Also if the antenna isn't in the clear with nothing shadowing it that'll skew the readings too.
I wouldn't take not being able to see a 50 Ohm impedance as an indication it isn't working properly. In fact when you look at say a 1/4 wave antenna over perfect ground with that you want to be seeing a 36.8 Ohm feedpoint and with a dipole 72 Ohms.