Oxymel of Squill wrote:
it's called damping off, I think it's a viral problem. It always happened to
me until I discovered Cheshunt Compound
Make up a teeny quantity (directions on tin). Wet the compost as normal, sow
seed, give a light spray with CC. Give another light spray when the
seedlings emerge.
No long legs!

good tip - I'll keep an eye out for it