I stripped out some interior and checked to see if there had been any issue with water/coffee ingress to the SRS module, looked in perfect clean shape. Gave the connector a spray with contact cleaner anyway.
Cleaned out the filth inside the air quality sensor, not sure if that helped or not.
Fixed the sticky button on the stereo panel, or rather it appeared to fix itself – no longer stuck pressed in. Perhaps something got lodged in there and simply removing the unit was enough to shake it loose.
Reassembled, battery back on, still got an SRS message and can't clear it.
So guess I will book in with Moss Vale Volvo and hold my wallet very tightly.