Next time this happens could you please save the guider image (PHD2 menu: File, Save Image) and post it to the PHD2 Forum. Please also include your PHD2 debug log with your post.
For PHD2 to work with automated imaging apps like SGP, it needs to be able to reliably select the best guide star in the frame, and we believe it is pretty good at doing that based on our collection of sample guider frames that we use to test with. Ideally, you should never have to manually select the guide star. If there are cases that PHD2 is not handling, we would like to investigate, but we need to see the camera frame and debug log.