From my observations it has nothing to do with the transmission (it's sitting stationary in 1st gear), but rather with PCM programming re: the A/C compressor operation.
As to why a 2016 wouldn't do this, I'm guessing while the base PCM code for Skyactive is the same from 2012 to current, there have been numerous tweaks along the way, and certainly can believe at the 2017 MY when they were tweaking NVH from previous generation. If the same A/C compressor strategy routine is present for 2017 and newer NA or Turbo, then the behavior would be the same. As the bump doesn't happen at *every* compressor cycle, it would appear to be a minor software bug/race condition under some situations; i.e. maybe the PCM is fussing with emission monitors, or timing a canister purge or something else when the HVAC interrupts it for an event. Agree only the software architect would know.