LED downlights glow when switched off
"Smart" switches use solid state (electronic) switching devices called "triacs" in most cases. The problem with triacs is that they don't completely turn "off" because the solid state nature of them has a very tiny amount of "leakage current" through them. When used on incandescent or even CFL lamps, that leakage current is irrelevant because the circuit can't really do anything with it. But LEDs take so little energy to illuminate that this tiny amount of leakage is enough to keep them glowing a little bit. The only way to stop it is to have a hard "contact type" switch that makes an air gap to isolate the LEDs off line. But those are typically not your "smart" switches. I have heard people say they can add one incandescent lamp to a fixture and that problem goes away, but I've tried it and it causes other problems if you try dimming.