Last night I have been imaging the Bubble Nebula, which is quite close to the celestial pole, so I tried my best to polar align my mount (GEM28) well. I calibrated the guiding around Deneb and slewed back to my target. At the beginning the guiding was acting a bit wild, then around 22:22 it settled down, then a meridian flip happened, and after that there was a period of normal guiding performance. Unfortunately after that the guiding went really wild again, I checked for cable snags and stuff like that, but there was nothing wrong. I tried to recalibrate the guiding after the flip but it didn't help at all. Any ideas on what might have gone wrong? Also, I'm wondering why the SNR was jumping like crazy sometimes.. it seems to be connected with bad guiding performance. I'm attaching the log file and screenshot from this night.