Thai Peppers – question!

Hey there,

My Thai pepper plants are coming along but I've noticed some of them have started getting mushy leaves on the lower leaves but the top leaves feel fine. I don't see what is causing the issue but hopefully some one else might know. The main one from the first 3 pictures has only just started to grow peppers while the 4th pic just shows how far along the others generally are.

I have about 16 pepper plants and a few other herbs growing under a viparspectra grow light.

Thanks!