Welcome to RIU. You didn't mention where you are located or what the temperature is in your space. I find in winter, with cooler temperatures, lots of things slow down. Healthy mature plants already kicking right along seem to take things better but if seedlings get too cold, too warm, too wet or too dry they slow down.
Oh, how about the humidity? Too dry? They will slow down. Seedlings can slow down anyway, so in winter, they can slow down even more.
Bottom line could be just being patient. Often the best thing we can do for our plants is get out of their way.
Good luck!