It happens when the air is not pointed straight at the horizon and it's angled down some. It's fine and there is a you tube video somewhere in forum on it and it explains the whole thing. I also have gotten that so I googled it and found the you tube video. If you Google mavic air warning attitude to high you can find out all the info.
I've seen some really cryptic messages ("Secondary flight control active") that, without explanation, might as well be displayed in Chinese.
Why issue a message at all, DJI, if the pilot has no way to understand its meaning?
Every message I have seen either personally or on the forums is very self-explanatory and tells you exactly what to do. Something like a numbered USB error though, yeah it would be nice to know exactly what it meant. In my opinion if it warns you about anything, it's time to bring it home.