Problem with tracking 2 axis, frame N-S

[stesigno]

Good morning,

I have a problem modeling a tracking 2 axis, frame N-S (axis tilt 0°, axis azimut .45°, frame phi +/- 50°, tilt frame 0/90°)

As you can see from the image attached, especially during cold months, early in the mornings, the tracking arrays show an incorrect position (phi angle +50°, tilt about 80°) with respect to the optimal position in which they would optimize their irradiation (phi angle -50°, tilt about 0°).

Am I mistaken the setting of any parameter or is it a software's "bug"?

Thank you in advance, kind regards.

Stefano