They could be needing minerals from water which the rain posesses.
Fox farm soil usually has nutes in it already and it might be burned.
Or its heat stress.
If you can put them outside or back on the window and wait a little more.
& If you can get a picture I could give you a way better answer.
Also alot of grows die because no one invests in a pH meter.
A pH meter is the most important device in growing and without it is like not having water or oxygen or light lumens for the plant.
I Suggest getting one of those.