the disappearing pea seeds!

I think I may be struggling to gauge the right level of moisture in potted peas. I potted some up - one seed to a 3" pot as a second wave recently, but only half have come through.

On investigating the ones that didn't emerge, I couldn't find a seed in any of the pots. The compost was slightly moist so I don't think they rotted - no tell-tale sign of pasty seeds - and no sign of digging on the top of the pots.

I wonder of I got them too wet one time and they have rotted then the compost has dried out.