It's weird how many clones I've had fail the last couple of months. The only really different thing has been giving them more (too much?) light just because I had room for them under the LEDs. These latest are under regular ceiling LEDs instead of grow lights. That seems to be working better, just not as well as in the winter.
Maybe it's too warm. I keep them on a seedling mat with the temp set to 80 degrees. It came on pretty regular in the winter, but not now, since it's always warmer than that in the shop where I keep them.