[BoorishBears]

Besides the CAN bus there's also a lot of other steps along the chain, their in-vehicle comms network, the uplink they're working with

Waymo's own systems are sending the current volume and HVAC settings to the OEM CAN bus every tick (presumably because the HMI's traffic is very low priority and may not be delivered on their network), maybe the trunk release doesn't tolerate repeat activations because of some quirk?

At that point obviously I'm guessing a bit, but the fact this issue has been prominent for so long makes me think there's some platform-specific quirk that's making it more complicated than it looks from the outside