Hello 
im using an Bambu Lab X1 with PETG-CF Black Filament from Bambu.
Until a few weeks ago, everything worked fine with it. Unfortunately, I now have quite big problems when printing standing walls. Almost every time i print them, there are always strange holes / bumps in it like this:
At first I thought it was something with the seam position because it always starts at the same place, but actually the seam position is on the inside wall and not on the outside wall and can’t have anything to do with it. But I still tried random seam position and this is what I got:
Then I tried printing the wall rotated by 90 degrees so horizontally like this:
instead of vertically on the print bed, after which the print looked good again.
But at the next bigger print everything went even worse:
Large holes are now appearing in the outer wall, but strangely enough it only starts from about half the print.
I have already changed the hotend and reduced the speed of the outer wall from 200 to 120mm/s, but it doesn’t change anything. I hope someone has an idea what else could be causing this.