So it seems recently Google pushed an update to Google Home. Included in the changes were evolutions to the automations. Unfortunately this broke key automations for me (keeping a heat intolerant person cool), until I debugged the reason.
I had automations which turned on the AC, turned it to Cool and set the target temperature, when the temperature reached certain time dependent thresholds. This stopped working recently, and editing the automation made no difference – it was just no longer triggered.
Turns out I needed to create the automations again from scratch, at which point it asked for new information which showed the triggers had changed (a breaking change in the existing automation triggers).