So the big bolt marked 12 N*m is tightened to that, but then take the 4 bolts underneath it to 5 N*m. That should snug it up for you. If not throw some carbon paste in between the seatpost and the clamp. I've been riding only on QR seatposts since 2010 and know this feature can be annoying, but if you go through the steps, it should stay set.

Agreed. You need to tighten the four bolts on the bottom of the seat clamp to keep the seat from rocking up and down.

Removed everything, made sure it was clean, no obstructions, applied Tacx assembly paste, reassembled, tightened alternating both sides then torqued the main bolt to 12nm and the underside bolts to 8nm and zero change in the play.

As soon as I figure out an easy way to embed a video, i'll post that as well.

https://youtube.com/...?si=FU-C6eZP8rNEd7HS