You're losing momentum because a lot of your mechanics are off.
First, read this. There's a lot to digest so take your time.
https://8limbsus.com/muay-thai-thailand/golden-kick-how-to-improve-your-thai-kick
Now that the info is fresh in your mind, watch this gif and pay close attention to the base leg, hips, and overall alignment & posture. Note the timing of when the base leg pivots around to open up the hips and align them with the target, draw a line through both hips and it points at the target, that's what you want. The upper body also stays fairly upright and it's not twisted relative to the hips. The kicking leg is accelerated and pulled through the target by your hips & body.
What you're doing right now is rotating way short and then trying to lift & push your kicking leg into the target with your hip muscles alone which loses a ton of power & momentum. Your hips look about 30° short of the target and your upper body barely rotates around. Your body ends up holding the kick back instead of helping to rotate & drive it through.