20M has been completely (totally) dead after nightfall the last few days. I wondered if I had a problem. So don't feel alone.
It may sound that way to some, but in reality 20m hasn't been closed or dead after nightfall; however the propagation is really closely following the sun for the past few days, and when night falls, you have to aim "west" to get propagation.
Here in CA where I am, around sundown propagation to the east collapses; I swing the antenna west, and the band's still fine looking towards Hawaii, the Pacific Islands, VK/ZL, etc.
This can change at any time, of course. But these past few days have been like that.