6 days ago, I repotted some chilli seedlings after they started showing their 3rd pair of leaves. They were the biggest seedlings at the time. Since then they seemed to have stopped growing. These are the ones in the green planters in the picture.
I left some of the slightly smaller seedlings in their original planter. These are the 4 seedlings in the black planter in the bottom left of the picture. You can see that they are doing much better than the ones in the green planters.
I found a question about stunted seedlings, but mine don't look malnourished:
What can I do to get the green planter seedlings growing again?
It took a while, but my chilli seedlings have started growing again. I have been lightly fertilising as suggested, I can't say that it definitely helped, but it certainly didn't hurt the seedlings.