What I 100% figured out, by writing the small code is the 18F issue with ST7920 LCD.
When I turn on the graphic mode, by sending LCDOUT $FE,$2E , there are high chances that random character in text mode will be displayed in top left corner.
I tried adjusting timings and OSC settings - no change. Same code, same PCB, same LCD - no issues with 16F1939.