Hi, bro!
I had the same thing with Gorilla Glue auto from FastBuds. I did LST after forming 4-5 nodes in week 3-4. After that, it immediately slowed down growth, and in the end, the plants were between 20cm and 30cm. Now I'm doing it without any techniques, and by week 5, the growth is already between 48cm and 78cm.
I concluded: autoflowering strains don't always respond well to training; you need experience and knowledge of the strain, and if you're going to train anyone, it should be photoperiod strains. Peace.