How is portal ownership decided?

I have a portal where this happened:

Player A conquered the portal, placed one resonator. Player A was listed as owner.
Player B, C and D placed more resonators. B is listed as owner.

Currently there's still the one resonator from A, two resonators are from C, five resonators are from D. And two mods from B and one mod from C.

So how is portal ownership (for the Guardian badge) decided? Is the owner the player who initially conquered the portal and still has one resonator in it or can it change?

achievements ingress

Best Answer

What you have seen can happen if you are player A, and for a short time.

If two players of same faction place a resonator on an unclaimed portal at about the same time (no more than a few seconds delay), A may see its resonator and its name as owner on the portal, then see it switch to the other player B. That means (I suppose) that on Niantic server B was first to place the resonator, but locally on A scanner the portal status is wrong for a few seconds.