I had a bag of potting soil I bought last year that was super moldy looking inside when I opened it up after sitting a year
It was stored inside and the moisture content must have been too high when packaged. Only time that ever happened to me. I don't know if it was a leaf mold or something nasty. Also, you never know if a bag is carrying any disease.
In regards to lighting, duration per day is a factor also. Plants don't like too much light if the soil is dry. They will droop and later some of the leaves will shrivel/dry.
Aphids usually hang around if there's a good meal to be had.
Too much fertilizer will definitely cause the symptoms you had.