Messy print

[Miatpi]

It's closed and Kisslicer don't give me any error messages at all. So it's at least not the model which is the problem.

Yes and no. The problem is that you are printing the model hollow, so you have serious overhangs not only at bottom surfaces but also at the top surfaces. The print is small, so you can get away with it - as you say, it prints okay with just one loop. But with two loops the loops interfere. Sometimes this helps, as one loop can give more hold to the other, sometimes it is bad as one loop might be pushed over the brink by the other, so to speak. Regarding the loop order (outer first or last), the choice is tricky as, in your model, you always will have overhangs where the first loop is better supported than the second loop, and vice versa.
Cooling seems also to be a problem here, so all in all I see the following options. Use lower extrusion temp, print slower, set the cooling fan at 100% all the time, reduce the extrusion width (and possibly layer height). Less extruded volume at a time, that is having a thinner thread, cools quicker and has less tendency to drop and pull the rest with it). But foremost, obviously, use sparse infill or support. Ah, and pick the seam position wisely so it wouldn't be just in the middle of a problematic overhang/bridge.

Thanks you!
And might my m227/m228 settings also be a part of the problem?

They are:

m227p: 0.03
m227s: 0.3

m228p: 0.0001
m228s: 1

Thanks for helping!

[Dreide]

And might my m227/m228 settings also be a part of the problem?

I don't think so. These setting just determine the look of the seams and are independent of the number of loops, so if they worked well with one loop...