What you are seeing is a fixed pattern noise that is actually being reinforced by your many, short subs. This is called “walking noise”, especially common with cameras of this class when used for AP due to their sensor noise characteristics.
You must dither more frequently. For non-dedicated astronomers camera, you will also want to dither a fairly large amount. Dithering every 30 minutes is effectively not dithering at all.
Things you should aim for to help fix your image:
Dither often (every 5-10 frames is a good target) and large (~20-30px, anything larger and you’re cropping a lot)
Inspect calibration frames for fixed pattern noise (up bias to 200 frames, ensure flats do not capture artifacts from your light source like LEDs by increasing exposure time to ~2s)
Use dark-flat calibration frames to improve your flats and reduce the chance that’s what’s contributing
If you are using the same calibration frames from your success on Orion a few months ago, there’s a chance they are poorly matched now due to differences in ambient temperature, camera settings, etc which could explain poor calibration performance which could result in walking noise like this
Depending on other factors, like the moon/light pollution/etc, you could be stretching this image harder than you did for Orion, which could also result in the walking noise being more pronounced in the final image
Ensure long exposure NR setting in your camera is off, in body stabilization is off, mechanical shutter is on…sanity checks for your camera specifically
ISO 6400 is high - learn about ISO invariance, your camera (source: https://www.dpreview.com/reviews/panasonic-lumix-dmc-g85-g80/7) will yield the same resulting photo (from a noise perspective) when set much lower, without limiting your dynamic range…ISO 1600 is a good rule of thumb for DSLRs in my experience
Use winsorized sigma-clipping for stacking
As always, the name of the game is longer exposures! Aiming for 30s or more would benefit you a lot. When working with a DSRL and more/shorter subs, the quality of your calibrations frames becomes very important and dithering often is essential
Late to the party but wanted to help:
What you are seeing is a fixed pattern noise that is actually being reinforced by your many, short subs. This is called “walking noise”, especially common with cameras of this class when used for AP due to their sensor noise characteristics.
You must dither more frequently. For non-dedicated astronomers camera, you will also want to dither a fairly large amount. Dithering every 30 minutes is effectively not dithering at all.
Things you should aim for to help fix your image: