In my 2-layer PCB design, I faced an issue where the GND copper pour did not fill around the STEP, DIR, and EN signal traces near the stepper motor driver headers (M1/M2). Even though:

• All GND nets were properly connected in the schematic
• Copper pour was assigned to the GND net
• GND poured correctly in other parts of the board

The area around the stepper signal traces remained unfilled when "Keep Island" was set to No.