Regular Pimples on the printing Surface

Hello Guys,
I have some Problems with regular pimpels on my surface as you can see on the picture. G-Code is also enclosed


Hard/Software:
- Marlin V1.1.8
- Rambo 1.1
- Repetierserver
- Raspberry
- Simplify

What I have already tried/learned:
- The pimpels are always on exactly the same position
- It seams that the printhead is slowing down before the pimple. I can see and hear it a little bit
- It just happens at a circle and not on straight lines
- I tried it on 2 simular and one different printer Hardware. All the same
- It has nothing todo with the Infill, I also have the Problem, when I Print just 1 Perimeter and no infill
- Speed has no effect on the position of the pimple, just on the look. Tested 50%, 100%, 200%
- Jerk Standard: M205 X10 Y10, tested: X5;Y5, X30;Y30, X60;Y60 no difference
- Extrusion Amount has no effect. Tested 80% 90 % 100% 120%
- Material has no effect. Tested with ABS and Ultem
- One idea was that the firmware doesnt get the G-Code fast enough. So I took my laptop and printed over "good old pronterface". Nothing changed


So at the moment I have no more idea what to test to get closer to the root of the problem. I would be happy if you can give me some hints!

best regards from austria
Markus