每日吃瓜

I have just recently started getting into indoor 每日吃瓜 and bought myself Ficus 每日吃瓜 and Sageretia 每日吃瓜. I have been taking care of them quite frequently by misting it every 3days or so, watering them when the soil doesn't feel moist or looks dry and bought a tray with pebbles to keep the humidity up. Since my room does not get a lot of light I bought a growth light which works with bonsai and use 4hours everyday.

The plant seems to be growing out new leaves and everything is looking good but recently I noticed that there are a few new leaves here and there where they have not even come out but became brown and hard (see the screenshot attached). What could be the cause of this as I am sure I am not overwatering the tree since I put my finger about half an inch into the soil and if its dry then I water it and I also keep the humidity up and my room is around 20-22C most of the time, could it be the growth light?

Please do let me know and thanks!

I guess the picture did not attach so see the image on this link: