Tommy seedlings.

Can you post a photo - and a close up of a leaf / tip perhaps?

These are not the worst of the bunch TBH.

Re-potted too soon maybe? The seed leaves there are bigger than the true leaves. I wait until my seedlings have at least 4 true leaves and are about 15cm tall before I disturb them.

Just a thought?

I'm having the same problem with a few of my chillies and with my aubergines. Really not sure what's happening as it's not happened the last few years and I don't think I've done anything different. Do you have many fruit flies? I have quite a few and am wondering whether they came in with the (different) compost.

Shouldn't matter provided that the compost isn't kept too wet. I've pricked out seedlings that are only a day or two old, no true leaves for some time after; only real risk, at that stage, I think is that there is so much compost in the pot, relative to the plant size, that it is easy to over water.

I wonder if they are getting scorched. Some indication of scorch on the leaf in the second photo. But they basically just look unhappy

What brand of compost is it?

How often are they being watered? They might only need once a week for that plant size in that size pot.

I had this with a tomato plant the leaves started dying off starting with a seedling leaf and moved up one after the other weird
When you transplant them is there any chance you've damaged the stem?

At the time the pics were taken, they had only been watered once from the bottom for about 10 mins. The compost has plenty of vermiculite in it so it drains very well. Compost is Jacks Magic. No sign of fruit flies. Romas done exactly the same way are nice and healthy. Ferline aren't too bad. The Alicante and Gardeners Delight set off best, but are now the worst. Since the pics, I've had to ditch a couple of plants and I've set some new seeds. Regarding scorch, that may be part of the equation. They were on quite a suuny window ledge and with the recent sun, it may have been too much for them. I'll try leaving the next lot a bit longer before transplanting as well.

I had simular problems, specially with Ferline which ive found to be hugely temperamental.

I would put them away from windowsil and just give them a week in a stress free enviroment to see if they perk up, mine did albeit still not as robust as some others.

The allotment diary chap on youtube recommends you transplant early a few days after the seed leaves appear so there is less root disturdance so I might try that next year, also mine seemed to do better once transferred into normal compost as oppose to seed compost.

I use mad jacks for the seedlings as well as the potting on. It's very fine so it should be ok. I just add more vermiculite for setting seed in. Its after potting up the problems start. I think the window ledge is favouite culprit. If the sun gets too fierce, it's too hot for them, and being near the windowpane they are getting scorched. The Roma must be mere capable of handling these conditions.

Couple of thoughts:

On windowsill is there any chance they are getting cold at night? (Seems unlikely at this time of year though ...) Behind a curtain with single glazing on a cold night ... the windowsill would be getting cold I suspect.

Re: pricking out early. I do do that, but the books say to wait for the first true leaves. However, I have changed what I do over the years. I now prick out to very small modules - a bit less than an inch square. My intention is not to give the plant too much water, and I have found that putting a seedling in a larger container (I used to use 3" & 9cm pots) made watering more difficult - fine if you have time to check each pot individually before watering, much harder if you have lots of plants and need to water them "all the same".

Nowadays I pot-up from the small modules into 9cm pots when the module cell is nicely full of roots. Its an extra step, but my losses have fallen from say 5% to almost nothing. Takes up less bench space early on, too.

Re: Vermiculite - not sure about that as my view is that it holds water, rather than improving drainage. I use Perlite (about 10% by volume) to keep the potting compost "open" and free-draining. Downside is that the rootball is much more inclined to fall to bits when potting-on / planting-out, which I suppose shows that it does indeed keep the compost open!! and I definitely don't have compaction of the potting compost as I used to when I used it "neat".

But I'm not convinced that any of this is actually a solution to the problem that you are seeing (unless you now tell me the plants have possibly been getting very cold at night)

I move the plants off the window ledge at night to avoid the possibility of them getting cold at night. I'm more inclined to think its the heat during the day. The problem here is they need the light.