while flying, mavic looks down sometimes (and what SD for Android S7 edge?) and APP update?

[Fazz]

hello again my dear pilots
These days i ran into a few problems... so i was thinking, any question answered is a big help!

1)these days when i'm flying, my gimbal suddenly looks down and i have to center the view by moving the left hand upper dial　（happens once per 3 batteries/each time i go out）

2) What SD card should i get for android? im confused for those U1 and U3 and whatnot

3) App update affects the mavic? is the same as firmware or?

Thanks !