Recently, Freefly has investigated multiple issues of degraded position hold performance that were caused by an unstable initialization (typically the machined was yawing while booting).
The ALTA needs to remain stationary with no movement immediately following power up in order to establish gyro offsets and calibration. Any movement during this time will cause a degraded (or failed) initialization. The ALTA does a series of self checks to ensure it is not moving excessively, and will fail the boot up procedure if so. However, in some instances the ALTA can pass these self checks even with excessive movement, which then leads to degraded position hold performance.
Freefly will be updating the ALTA firmware in the future to increase the robustness of the ALTA boot up.
Keep the ALTA stable and stationary while booting. Often the pilots at Freefly will use one of the foam prop protectors to wedge between the ALTA and the Gimbal to ensure the aircraft does not spin / move on boot up.