2,5m cable too long for LCD connected to Arduino UNO?
If the interface you're using is I2C(only two cables from arduino to lcd, vice versa)you have a problem,you need to pull up the sda-scl channel with appropriate resistors, you could (maybe) boost the I2C signal using ti-p82b715 bus extender, I just assume you use I2C (2,5m length?), what interface do you use? SPI? I2C?