Sweetcorn seedlings dying off

Hi all,

This year I sowed the rest of my packed of Incredible F1 in the hope of finally growing decent sweetcorn. The seed sprouted well and grew to a few inches high. Then the seedlings started keeling over. They didn't have what I think of as the usual signs of damping off - overly damp soil and withered sections of stem. I planted them out and even the decent looking ones have died (three survivors out of 30 or so!). I've ordered some more seed and I'll try again – my daughter loves it and we were so excited to grow it this year that I will even look at buying plants if the new seed doesn't take off or is looking too slow to develop.

I've never had luck getting my corn to the plate, but I've also not had problems at the seedling stage before. They were going downhill before transplant so I don't think it's to do with transplant shock or root disturbance.

Any ideas other than damping off? Pro tips to avoid problems with my next batch? Should I just chit them and then transfer to the plot instead of growing into little plants first?

Thanks!