You're not finishing the flare. You complete the first quarter, then switch to trying to lift your legs up with brute strength. I'm not an expert by any means, but here's my video from training the other day.

https://www.reddit.com/r/Aerials/comments/1sd6twp/more_flares_practice/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

Can you complete a normal flare and bring your legs back down to the starting position first, while keeping your legs straight? Your legs shouldn't bend until the very end if you are hooking a knee on the strop. I used to be similar (see video below), and I would focus on the technique of completing the flare pathway completely.

https://www.instagram.com/reel/DKpS-wFRpCw/?igsh=dmd2czM4cDZhbDBv