Larry - I think you hit the nail on the head. When I was looking at your photos, dry soil came to mind immediately.
In my daylily beds that get constant watering and even a little shade during the day, none of the seedlings have disappeared except one. (It is completely gone!) They all have various parents, so the likelihood of at least some of them going into summer dormancy should be in the 70+ seedlings, but none have, so .... water is key to a happily growing plant.
