Does AD680 have high impedance mode?

We designed to connect AD680 to four AD7741 at 2.5V.

When the pull down resistor was 20kΩ, the voltage of AD680 drops from 2.5V to 2.35V. And when the pull down resistor was changed to 500Ω, the voltage drop was eliminated.

Why is the problem solved?

Is this because the AD680 has a high impedance mode?

Please tell me m(-_-)m