I highly doubt a software update caused this, a loading of the AT&T network in your area, which can cause network operators to substitute a lower fidelity voice codec to conserve bandwidth, is the likely culprit. Voice recognition needs good audio to function correctly. It works amazingly well here right until I'm about to go out of cell coverage and then it starts misunderstanding me as I imagine the audio must have the same little dropouts I get when making a voice call that voice recognition cannot handle.
Another potential explanation is if the microphone was disturbed so it was picking up vibrations from the car.
There is no reason why whatever software Tesla uses would be worse now vs. then. It's audio quality that VR needs to function well.