Plants dying in Jiffy peat pallets

I have started some vegetables in these Jiffy peat pellet trays. I am finding that some of plants are getting long and then the stem looks like it has been stretched. It then dies. I am keeping it watered. I did have a fan on them while they were inside. Now I am putting them outdoors during the days.

Pictures is the Brussels Sprouts but the Rutabagas have done the same thing.

Does anyone have any ideas?

It looks like damping off, despite the fan. I'm not sure what you can do except try to make it a little warmer and dryer (but keep the soil moist).

To me, those plants appear what is called "leggy". Extremely looong, skinny stems.

That usually indicates insufficient lighting. They are stretching out, looking for their lifeblood...the sun.

When I raised a bunch of seedlings under some standard florescent lights, they all looked like that.
When I switched to 'Daylight' bulbs (full spectrum), they almost immediately began 'normalizing'.

Some people swear that 'full spectrum' bulbs are a waste of money, and are not necessary.
My personal experience shows that they promote a healthier plant, ready for x-planting much earlier.
In my opinion, using an improper bulb is the true waste of money. You get what you pay for.

My experience with the jiffy brand is that it does not hold the moisture.

This exact same thing happened to me once before but I am unsure if my tap water from the city supply had some effect. I would definitely invest in a full spectrum light though.