Richard, no details or insight here, just a load of BS / euphemism being shoveled out by CAISO to cover for the failure of gas and renewables to provide reliable electricity. For example:

"While recovering our ACE, a generator ramped down quickly from 400 MW" (subtext: the generator, a gas plant in Edison's service area, ramped down quickly because it ran out of gas, because CA pipelines can't provide fuel to gas plants fast enough to meet late afternoon demand after the shutdown of San Onofre Nuclear Generating Station).

Or:

"5:15 PM Dispatched approximately 800 MW of demand response to maintain load and resource balance" (subtext: raised prices and thermostats to force customers to bear the burden of insufficient, unpredictable generation from wind and solar).

I'm speculating that the call for DR at 5:15 failed to meet the 800 MW dispatch instructions, which lead to the stage 3 emergency declaration at 6:36.

Have you read any longer term studies that have analyzed how often DR calls are successful compared with different levels needed, different times of day, etc.? I would assume those in utilities track this closely, but I'm curious if there's a look at across the whole sector what has seemed to been the underlying reasons certain DR calls fall short.