Partial underextrusion in walls I'm facing weird "pillars" of underextrusion on outer walls of my XYZ test cube.

On the pictures below I`ve printed PLA test cubes with a 0.4&nbsp;mm nozzle, 0.2&nbsp;mm height and 210/50&nbsp;&deg;C hotends/bed temperature.

Gaps are appearing in walls parallel to both X and Y sides. The pictured side is parallel to Y face.

I'm slicing with Cura, my printer is a homebuilt around Anycubic Kossel with Marlin 2.0 onboard.  

What have I tried already:
1. Temperature from 190 to 210&nbsp;&deg;C
2. Retraction from none to 6&nbsp;mm 60&nbsp;mm/sec
3. Tuning down Jerk in Marlin from [10,10,0.3] to [5,5,0.3]
4. Tuning down acceleration from 3000 to 1000
5. Tuning print speed from 60 to 30&nbsp;mm/sec
6. Checking belts, nozzle and extruder.  

Now I just ran out of ideas. Delta is calibrated by G33 autotune. Mechanics looks just fine. What am I missing?




UPD1: tried removing combing - it did not help. But I noticed that my printer accelerates strangely at this parts

UPD2: could it be stuttering? I have 320 segments per second with block buffer size of 8 bytes(?)

UPD3: lowering segments count to 120 and raising block size to 32
Localized underextrusion usually means you're oozing material somewhere it wasn't supposed to go. Since you have Marlin 2.0, linear advance might help solve that, and in general right retraction amount is important and turning off combing may be needed (combing over infill allows material to ooze).

Also there are reported bugs in Marlin 2.0 such as  https://github.com/MarlinFirmware/Marlin/issues/15473 that might be related, though I would think you'd not be using junction deviation since it's supposedly incompatible with deltas.