The one where the seedling is down looks like damp off from too much water to me. I don't know what signs you are referring to. There is often no more sign than seedlings dying off.

I don't know what soil mix you are using but it might be that those trays that are dying have components in the soil that retains too much water.

Put a fan on them and cut back a bit on the water

Alyssum is the only thing I have ever sown under lights that succumbed to damp off. A similar situation where some containers did fine and others were completely wiped out - or mostly.

I know thats not helpful, except to let you know that sometimes these things happen even when you are doing every thing right.

Think I solved the issues - lights were too close and were over heating soil-less-mix and frying the cotyledons - cool season seedlings like to be cool... -face palm-

Update - Turned out this was an old/batch of seed. Supposed to be receiving a replacement soon. Grrr