Long ago, I had a similar problem, then realized there is a "calibrate" command that's different from the "reset/level" function within the Stratux interface. Here are the instructions I got from Chris Young (the main Stratux developer) when I ran into trouble:
There are calibration values that are measured from the gyro when the unit is first started up. If the unit was moved during this first-start routine, it could potentially cause this issue. If you still have the chip that exhibited this problem, try plugging it in, setting it level, and then go to the "Settings" menu and "Calibrate Gyros". This is a different function from the "Reset/Level" function on the GPS/AHRS menu. I'd be curious to know if the unit calibrates correctly, if not then this is a new issue for us.
Performing "Calibrate Gyros" on the Settings page did in fact solve my problem. If this is what you've already done and it didn't help, then I apologize.
One further option you could try is posting a bug report in the Stratux project at GitHub, here: https://github.com/cyoung/stratux/issues . As he mentioned in his correspondence with me, Chris would be interested to know if there truly is some new anomalous behavior occurring.