That PDF shows the default wiring on the MB-6582 base PCB… HOWEVER the resistor is connected to the PIC pin AND NOT the J15 pin, it is NOT needed for the LCD.
You aren’t usng 4-bit mode on the PIC18F452 Core, therefore you have only proved it works in 8-bit mode on the other Core, and not proved that 4-bit mode works for these displays. You can try moving the PIC18F4685 to the other Core, and disconnecting the unused four data wires on the LCD (I am assuming if you’ve tested it on the PIC18F452 then you must be using a cable with all 8-bit data wires connected). This will test these displays work in 4-bit mode.
Also, check connectivity between J15 pins and the PIC pins. Maybe there is a short or a break.
Finally, R80 should be mounted for the CAN bus, but it should have no effect on whether the LCD works or not because it should not be connected to J15 at all… likewise with the diode that connects the CAN bus Tx/Rx pins on port B, these are not connected to the J15 pins and thus not connected to the LCD.