Yeah, the pre-fertilized soils will kill em too, especially if they're being watered frequently. I was thinking that the 50% perlite might have cut the ferts down some from being at a fatal level for seedlings, but maybe not....

When planting germed seeds, its best to NOT pack the soil firmly. Leave it sorta loose in the containers. Then when you water before planting to moisten the soil, water until it runs out the drain hole/s. That will settle the soil.

Its also possible to flush the newly planted seeds out with a heavy watering, so i use a spray bottle to add moisture the 1st time or two after they are planted, or until they actually sprout and begin growing a taproot and get anchored to their world. Peace at ya.