I have a small problem while printing these plugs.
As you can see it creates some artefacts.
The strange thing is that it happens only at one side and on one of the two printed objects.

I think there could be several problems:
It's printed in ABS 210/100 (I tried some lower temps) and it show a little dark spot, like it's burned (or irregularity in the ABS?).
The table it's placed on, moves a little while printing, but why is one side still good?

Who knows the answer?

This looks to me like your esteps/mm is much too high.

Once you get that worked out, see about using your slicer to adjust your print speed down on the layers that go by too fast, and make sure you have a fan to cool the print. You're putting down plastic on a layer that hasn't solidified yet.

Thanks I will get into that, right now I'm running the basic setup that was given by the manufacturer.
But does this explain why one side of one part has no problems at all?

If you watch the printer as it does a print, there is a pattern to it's movements. It will do a different set of motions as it goes through a layer. High speed will throw off some of those motions. A combination of too high moves and a bit of ooze from the hot end would explain what you see.