Karen, sorry you had this and yes its moisture.
I moisten compost to 100% when I have just sown seeds, then nothing for a couple of days (unless blistering hot) and then water moderately until plants have some strong leaves, when they start to pump water from the module.
On cloudy days I water very little.
When raising plants, they all have different water requirements so its good to use a fine, even rose which enables accurate placement of water, more for some and less for others.
Best of luck with your new sowing.
