The two main ways this happens is:
-You exceed 150 degrees per second on any aircraft axis. When you're doing aerobatics, basically. In this case, the unit is in this mode as it figures out which way is up. A few seconds of straight and level flight is all it takes.
-The unit has non-zero airspeed when it is powered up. In this case, it assumes it is flying, and it goes into the same mode while it takes a few extra seconds to confirm the attitude solution. Same timeframe as above.
In both of these cases, low rates on all axes are required for a few seconds for the horizon to recover. Basically, straight and level flight, or close to it.
Also, note that the EFIS never "gives up". It keeps showing you attitude, and usually, it's pretty close, even in this mode.
So, I think the non-zero airspeed (presumably on power-up) is the issue here. Do you have anything applying pressure to the pitot, or pulling a vacuum on static?
