HomeKit accessories not responding

All of my HomeKit accessories (Eve Outdoor Cam, smart plugs etc) mysteriously stopped responding to Home.app a couple of days ago, and the usual remedial steps—rebooting everything, resetting and re-pairing etc—have been unsuccessful. The camera streams OK but will not record or obey automations so is pretty useless.

What else should I try? Has Apple changed something in HomeKit that might explain this.

Chris