I have same problem. Here's my observations:
I have 2 remotes and 2 drones. On remote that was taken apart and put together by me both drones flying at slight angle. On 2nd remote both drones flying dead straight.
Mine pulls to the right. You can clearly see it when you line up an object directly underneath you with gimbal facing directly to the ground and the drone flies slightly to the right. It's so annoying. My first Mavic didn't exibit same behaviour.
Mine also pull/slips sightly to the right while Flying /Videoing...
I compensate by Yaw little to left while trying to say follow a straight road
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It's forward and Left on the Right stick
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Possibly fix by Flying in Fix Wing Mode.?
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...........C
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Merely Physics! Try to point your car down the road and let go of the wheel. Yeah good luck going straight. We don't fly in a vacuum, so there's no absolutes.
Mine doesn't fly straight either but it depends on the day. If it's windy it gets pushed slightly in that direction by the cross wind so I offset it slightly in yaw so it gets pushed to where I want it to go.
Not much different when flying into a headwind, the drone doesn't keep it's speed, it slows down, if it's too slow I engage sports mode to compensate (which limits the flight time obviously). In a downwind, I gain a little as the drone doesn't need as much power to maintain its speed (or engage super sports mode and enjoy the rush