This happened to my externally routed KS Lev dropper seatpost, which was only a few months old. Ultimately, the problem was the external cable tightened up (cable was pulled towards the front of the bike) and caused the post to start sagging.
To fix the sag issue, first make sure the the cable of the KS Lev dropper has not tightened or loosened up especially where it connects to the dropper post. This could happen due to a crash, getting your handle bars twisted, or just from transporting your bike... especially if your KS Lev cable is externally routed.
After that, you may need to re-adjust the barrel adjuster on the cable to fine tune the dropper post.
Doing both of these things fixed my sag problem and got my KS Lev dropper post working like new again.
If that doesn't work, you may want to check air pressure in the post.