In the GCode viewer of version 1.6.1. Layer 1 shows the first layer, but Layer 2 appears to show the filament purge line???
This has occurred on files sliced on both Cura 4.9.0 and 4.9.1 (latest as of today) on the Mac.
This appears to be extraneous. Cura reports 85 layers for my current print, whereas OctoPrint is showing 86 layers.
There is no negative printing effect, just an extra incorrect layer in the GCode viewer.
GCode viewer layers are sorted by z-height. Your prime line is probably higher up than the first layer of your print.
Where would that even be set -- I know Cura's settings can be cryptically named sometimes, but...
Look at your start G Code ( Preferences/Printer/Machine Settings )
there should be the Gcode for the prime line.
in my case:
G1 X0.1 Y20 Z0.3 F5000.0 ; Move to start position
G1 X0.1 Y200.0 Z0.3 F1500.0 E15 ; Draw the first line
G1 X0.4 Y200.0 Z0.3 F5000.0 ; Move to side a little
G1 X0.4 Y20 Z0.3 F1500.0 E30 ; Draw the second line
and if you are Printing at a layer Hight of only 0.2mm and the prime line is at 0.3 it will show up as the second layer...
Great answer - it looks like you tried to use a code block, but it didn't render since it's not quite the right characters. Use triple 'backticks', like ``` and ```
My Ender 3 has done this since I got it and back to Cura 4.2