Hello!
Tell me how to solve the problem.
I switched on Osmo 3 yesterday, connected it to the phone, and saw that
the horizon line on the left dropped 2 mm down.

Maybe you can return the factory settings or reset?
But I did not find anything.

Gimbal menu, scroll down to horizontal gimbal adjustment. You can incrementally correct any tilt from horizontal.

Hello there zmitser. I am sorry for the trouble this has caused and thank you for reaching out. May we know what is the model of the mobile device that you are using please and as posted by DAFlys on post #2 please try to manually adjust the gimbal. Thank you.