Necessarily, whatever exists has properties, and necessarily, whatever has properties exists. So, necessarily, x exists iff x has properties. But it does not follow that existence is the property of having properties. Why not?
Peter and Paul differ in their existence. But they don't differ in point of having properties. They have different properties, of course, but they don't differ in respect of the property of having properties. So singular existence (the existence in virtue of which each is and is not nothing) is not identical to the property of having properties.
And yet very competent philosophers make this mistake. To name names: Dallas Willard, J. P. Moreland, J. K. Swindler.
One source of the mistake (though it might not be the source of the mistake in any of the above-mentioned) is the confusion of (broadly logical) equivalence with identity. Necessarily, x is triangular iff x is trilateral: there is no broadly logically possible world in which the extensions of the terms differs. But it doesn't follow that triangulariy = trilaterality. They are distinct properties despite their being necessarily coextensive.
So from the fact that nothing can exist without having properties, and nothing can have properties without existing, pace Meinong, it does not follow that to exist = to have properties.
Besides, is it not obviously circular to say that the existence of a is its having properties when a cannot have properties without existing? Think about it.