I manually switched my HS210 3-way light switch to "on" today and the lights began to flicker on and off. The lights no longer responded to manual on/off or to Alexa voice command. I turned them on with the second switch. The lights respond normally (on/off and dim) to this switch.

Returning to the HS210, I see that both the white circle indicator and the green WiFi indicator light are blinking, both rapidly. This continues 2whether the lights are on or off. Pressing the RESTART button causes the light to go out for as long as the button remains depressed and the flashing lights return when it's released. Pressing the RESET button does nothing. Holding it down for up to 30 seconds likewise has no discernible effect. Rebooting my router did not help.

This switch has operated perfectly for several years. There's been no power surge or other interruption at this location. All other electrical and bluetooth devices (including a number of tp-link plugs and switches) are working normally.

What should I try?