What frame and what seatpost do you have? Post a photo of the clamp, including the frame slot below it.
Years ago, on a previous bike when it was new, the seatpost was slowly creeping downward over time. I assume the force of riding over bumps contributed to this. But I never had the saddle twist sideways, or have the seatpost drop even 10mm. Something doesn't seem right on your bike.
~~~
Years ago, I got a tube of Tacx Carbon Assembly Paste, and still use the same tube now. I like it. It's no longer available.
I see Park Tool has a similar gel, with silica grit.
Park Tool Supergrip.
I use it on seatposts and on the handlebar-stem clamping area. It's effective. I don't need the full recommended torque on the stem clamp when I use the gel.
It works for aluminum to aluminum clamping, and carbon to aluminum or carbon to carbon.
~~~
To monitor any seatpost slippage, I used a silver Sharpie pen to draw a line just above the clamp. It will wear off eventually, so I would renew it occasionally. To remove, it, rubbing alcohol easily wipes off the sharpie mark.
Now I use thin 3mm wide strip of masking tape with a slight gap between the tape edge and the clamp. Any slipping is obvious since the gap disappears. (I'm not sure why I keep the tape on the post, since it hasn't moved at all for quite a few years. I did have problems with an older bike, years ago.)