agcc Actor fails centroid in a certain area of sky (detector) intermittently

(This has been observed for a long time, but was not reported clearly..)

While guiding, the stars in given areas were not detected (i.e. flag >1) intermittently.

This is one example: 

Here, stars on the right of AG3 and AG6 are flagged >1 in some frames.

The below is another example:

Here, stars on the right of AG2, AG5 and AG6 are flagged >1 in some frames.

This unstable measurement affects calculation of pointing error now, and especially cause large scattering in the field of less star.

Could you investigate the root cause and try to make centroid more stable?