I just had one fail exactly this way that has been in service since 2015. I was able to dismantle it and resurrect it by replacing C7 capacitor on the power supply (line connected) board. This is a small 10uF 25V electrolytic capacitor right beside the large inductor. Probably a 5 cent part, but “free” for me since I had a 10uF 35V on hand.
Dismantling and reassembly was straightforward but tedious because you have to desolder a 6-pin hard-wired connection between the two boards to gain access to the back side of the power supply board.
Unfortunately it seems now we cannot ever expect an electronic device to last much over 5 years because of the “capacitor plague”. Perhaps this is an inevitable trade-off required for miniaturization sufficient to have “smart things”. Maybe there should be a standard disclaimer for anyone just starting out in home automation that they will need to have an annual replacement budget for failed devices.