Hello,
i am printing large flat surface (plate): 210cm(W) x 201cm (L) x 2,5mm (H). Some technical characteristics:
Printer - Ender3;
slicer - Cura 4.4.1;
Filament - PETG black Devil Design;
built plate temperature: 75 degrees C;
nozzle temperature: 235 degrees C;
layer height - 0,2mm;
retraction - 6,5mm;
retraction speed - 25mm/s;
print speed - 50mm/sec;
combing mode - all;
fan speed at layer 1 - 0%;
fan sped at all other layers - 50%.

When printing first 2 layers, they were perfect: surface of the printing part is very even, no stringing. But at the 3rd layer strange thing happened: layer became uneven. It seems like the veins popped up from the surface. Also stringing occurred.
DSC_1316.jpg
I have no clue what causes this problem, because layer below corrupted layer is completely flat. I have tried to increase/decrease nozzle temperature by 5 degrees C, increase/decrease fan speed but these changes do not had any effect. Maybe someone have faced with similar problem?