Rotten tails on my sprouting seeds

A question from a fellow grower:

I did soak them in water first and kept it on a heat mat, all but two had sprouted tails, it
was only after I planted them I had problems. The tails went yellow
and mushy after a few days and they of course didn’t spout into
plants.If I could only work out what caused their tails to rot?

What did you plant them into? This is probably the issue.

I know a lot of people like to soak the seeds and get a pigtail before planting, but I start my seeds in either a rockwool cube or a peat pellt soaked in warm water. Works every time.