The ADA4807 input range includes the negative and positive rails. In fact it allows input 0.2 V beyond either rail.
Further, in the Theory of Operation section the datasheet says,
Specifications like input bias current, offset voltage, etc., might not be maintained with the input biased at the negative rail, but in general this op-amp should still act like an op-amp in that condition.
However, the minimum output voltage is 0.1 V above the negative rail. You'll also notice that the minimum output voltage in your transient simulation was about +0.1 V.
Therefore a follower configuration cannot maintain negative feedback when the input is at or below the rail, and the op-amp will be saturated at this bias point.
In saturation, very low AC gain is expected, and this is reflected in your AC simulation result.
If you arrange to have a negative supply available, or bias the input at least 0.1 V above the negative rail, you should see a gain of 1 for this circuit.