Here's an idea that might help with the dither or other drift issues...
Have a Drift Limit... Capture the first Alignment position and set a limit on far the image is allowed to drift. Once the limit is hit, Run a Re-alignment (like after a Flip) or Park.
I'm also thinking... what is done for a random passing cloud?
fsignoret: Dithering causes the frame to slightly shift between images. It is done to even out non-random noise. Depending on how aggressive the dithering is, it is possible to wander off the desired framing of the target.