Nathan wrote:
"Why wouldn`t they occur at the same time?"

Suppose you adjust the length of a 1/4-wave antenna to resonance. And,
suppose its impedance is 37 ohms. The antenna has no reactance and is
resonant but it does not match the coax in spite of zero reactance
because the surge impedance of the coax is not 37 ohms.

Best regards, Richard Harrison, KB5WZI