Welcome to the forum ScottE!
I have noticed the A/C is not as efficient at idle compared to when the car is on the move(in gear etc). But it is working, just not at peak efficiency.
This is evident on most cars. As the AC does add a significant load to the engine in terms of power requirements.
Similar concept would be how the alternator charges/runs the car electronics better while driving compared to when parked and idling.
2016 Cx-3, 2.0L petrol, manual transmission. South Africa.