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:

• 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

Try longer exposures, your mount can do 30 sec easily with a 300mm lens, even without guiding.

Also, go through your subs and remove anything that looks out of the ordinary. Better to have 600 good subs than 1200 with bad ones in the mix. Look for clouds and condensation mostly.

This sort of noise increases the closer to the horizon the target gets. Stay above 30 degrees if possible.

Check if your white balance is set to auto, if it is set it to something fixed.

Lastly, judging by the end result you should try a less aggressive stretch, especially for the background. You can make a mask of the nebulous part, stretch it a lot and then use it as a luminance and saturation mask over a copy layer that has a neutralized, darker background.

There’s lots of good signal in there, give it a go

It could also be that you’re not dithering often enough. Dithering every 30 mins means you’re taking 180 frames before each dither and that’ll really let the walking/raining noise build up. you could try doing 30" subs and then dithering every ~10 minutes if that’s practical? For me personally I dither after a max of 5 subs (or dither after a sequence of something like LLLLRRGGBB) , but I know I’m also taking longer exposures and have the benefit of automation.

Personally I’ve never used a GTi or Lumix camera, but if you’re able to hook them to a computer with NINA, there is an option to have it dither automatically even without an autoguider