It appears that the issue was in many cases that the Waymos were so timid that they created a much worse traffic jam than humans would have - and excessively impacted hundreds of human drivers in the process. Driving too slow and impeding traffic can result in a moving violation, perhaps other irrational behavior by a human driver OR a robotaxi should as well.
This is actually going to be very interesting as robotaxis become more common and are operating during rush hour while trying to merge into freeway traffic from on-ramps. When traffic is flowing at, for example, 40 MPH, there's often little space between cars on the freeway (in some cases significantly less than the "recommended" number of "car lengths"). In such situations there's sometimes no "completely safe and legal" way to merge - one has to either "rely on the kindness of strangers" to slow down a bit to leave gaps for merging traffic OR "bully" their way in. When neither works, somehow humans (almost) always work it out using social cues and mores.
The lawyers at the robotaxi companies won't like the "bully in" approach so the robotaxis are likely to be very timid and end up not doing that. Human drivers on the freeway are likely to be much less sympathetic to the robotaxi (after all, it's just software, not human - esp. if it's "deadheading" and has no passengers).
This raises the specter of the robotaxis just giving up and stopping at the end of the merge lane (after all, that's the only completely safe thing to do). Once at a dead stop at the end of a merge lane, there's little hope they will find an opening big enough. After enough robotaxis are backing up an onramp, likely no traffic can use that onramp until rush hour ends (perhaps hours later).
Admittedly, this will be somewhat self limiting - when all the onramps are blocked, traffic on the freeway will dramatically drop and there will be room for a few "robotaxi road boulders" to "merge" onto the nearly empty freeway and perhaps the backed up cars will flood onto the freeway creating a convoy effect.
This will create interesting strategies for human (and robotaxies). In such a scenario it may make sense to drive away from your destination many miles to get on the freeway at an onramp that is "upstream" of most traffic to avoid being stuck for hours on a blocked onramp. This of course will just increase congestion yet more on surface streets due to the extra traffic.
I guess the good news is Caltrans could just eliminate metering lights - the stopped robotaxis would (very crudely) manage traffic as a side effect.