Can you share some of your code so we can help debug the issue. I've used the backpack with several displays using both I2C and SPI and it worked fine.
Note: I have done a bridge in backpack pcb to enable SPI mode.
The code is from MicroLiquidCrystal, the HelloWorld Sample.
....
// Option 2: Use shift register provider
var lcdProvider = new Shifter74Hc595LcdTransferProvider(SPI_Devices.SPI1, Pins.GPIO_PIN_D10,
Shifter74Hc595LcdTransferProvider.BitOrder.LSBFirst);
// create the LCD interface
var lcd = new Lcd(lcdProvider);
// set up the LCD's number of columns and rows:
lcd.Begin(16, 2);
// Print a message to the LCD.
lcd.Write("hello, world!");
....
Regards, Pablo
