Hello my friend, this response is logic after transplanting. Your light is definitely not too strong and enough for this phase of the grow. But 18/6 schedule is better in my opinion. I did a few test runs with Autoflowers on 18/6 and 20/4 and 24/0 and the 18/6 gave the best results.
So long story short, this response is from transplanting. My advice change the light schedule to 18/6
Merry Christmas buddy! 💚