most prolly a photoperiod.It happen once in while: Time to switch to 12/12
"As you may know by now, after 3-5 weeks your autoflower should be transitioning to the flowering stage but if the weeks go by and you don't see any signs of stigmas (white hairs) there are a couple of things that could be causing this.
First of all, you need to remember that the information most breeders specify is when growing their genetics in optimal conditions so if you don't have a good light fixture, nutrients and are not controlling the conditions, your plants may take a bit longer but don't worry, they will flower."
source:
https://2fast4buds.com/news/how-to-tell-when-autoflower-is-flowering
and another interesting article you can have a look:
https://www.royalqueenseeds.com/blog-how-to-grow-autoflowering-cannabis-n83
hope that helps, happy growing