Please let me know what can be the reasons?
What drone?
You have posted in the General section with no indication what aircraft you are talking about. No explanation regarding the problem you are experiencing.
No elaboration as to what you mean by 'doesnt land properly'.
In order to be able to assist, we need information:-
What aircraft.....
What specifically is the scenario/conditions it occurs?
What are the symptoms?
Too fast?
Too slow?
RTH not working accurately?
Unstable descent?
Landing gear not lowering? (assuming it has retracts).
Bouncing on auto land?
Not landing at all?
Error message before landing?
Error message while hovering to land?
Refusing to descend on throttle down over landing area?
Auto land or manual land?
Since you appear to run your own UAV business, and your other thread was entitled 'Whats the best drone to buy' this seems more than a little strange.
I can only assume you might be trolling!
If you wish to discuss this via PM please feel free to contact me.
Alternatively, please be descriptive in your posts/threads and post in the relevant section so that people can actually offer help (assuming it's wanted).
Posting ambiguous and deliberately vague threads is not helpful.
Thank you