To focus on the question is: Why is the ground resistance so high? It
is not important at this stage to determine its precise value. The
point is it is high enough to cause a return of 0 degrees. This puts
the 'system' at over 50 degrees. Even if the antenna were 6 to 8 Ohms
the ground loss would be at least 42 to 44 Ohms.

Simple answer- add more radials. Especially if the impedance is varying
noticeably depending on ground moisture, you need more radials.

Another possibility is that if there is some other conductor in the near
field (tower, house, other wires, etc), the impedance might not be what
you expect.

Tor
N4OGW