Is it turning brown where it narrows?

It sounds like it could be overwatering, but I'm not too sure. A picture would be helpful.

Mark

Sounds like damping off, a fungal disease. Unfortunately seedlings of all kinds are vulnerable to it.

When I planted all my plumie seeds I used to drench once a week with Spanish water, which is just water with a big splash of hydrogen peroxide in it. I rarely lost any to damping off.

Good luck!

Don't panic. Mine had trunks right at the soil line, and then narrowed to the roots. As my soil was very coarse and airy, it compacted over a few months with more regular watering as they got their first leaves and a similar thing happened. I added soil back to cover the roots and help keep them propped up.
Not sure without photos.
You could pull one up and rinse the soil off the roots and inspect for rot. It will tolerate being replanted just fine.

Thanks everyone...I was pretty sure it was overwatering...I will try to send picture but I'm not extremely techno savvy.
L