Hi,
I have run a diagnostics program called I2CexpDiag.
This was the output from that run.
00:15:22.697 ->
00:15:22.697 -> ********************************************************************
00:15:22.791 -> Serial Initialized
00:15:22.791 -> --------------------------------------------------------------------
00:15:22.884 -> I2CexpDiag - i2c LCD i/o expander backpack diagnostic tool
00:15:22.930 -> --------------------------------------------------------------------
00:15:23.024 -> hd44780 lib version: 1.3.1
00:15:23.024 -> --------------------------------------------------------------------
00:15:23.116 -> Reported Arduino Revision: 1.8.13
00:15:23.163 -> CPU ARCH: AVR - F_CPU: 16000000
00:15:23.209 -> --------------------------------------------------------------------
00:15:23.257 -> SDA digital pin: 20
00:15:23.303 -> SCL digital pin: 21
00:15:23.303 -> --------------------------------------------------------------------
00:15:23.395 -> Checking for required external I2C pull-up on SDA - YES
00:15:23.441 -> Checking for required external I2C pull-up on SCL - YES
00:15:23.488 -> Checking for I2C pins shorted together - Not Shorted
00:15:23.629 -> --------------------------------------------------------------------
00:15:23.723 -> Scanning i2c bus for devices…
00:15:23.723 -> i2c device found at address 0x27
00:15:23.770 -> i2c device found at address 0x40
00:15:23.815 -> Unknown error at address 0x51
00:15:23.861 -> i2c device found at address 0x60
00:15:23.908 -> Total I2C devices found: 3
00:15:23.908 -> --------------------------------------------------------------------
00:15:24.001 -> Scanning i2c bus for all lcd displays (4 max)
00:15:24.095 -> LCD at address: 0x27 | config: P01245673L | R/W control: Yes
00:15:25.303 -> Total LCD devices found: 1
00:15:25.303 -> --------------------------------------------------------------------
00:15:25.397 -> LCD Display Memory Test
00:15:25.397 -> Display: 0
00:15:25.444 -> LCD stuck BUSY status
00:15:25.444 -> --------------------------------------------------------------------
00:15:25.537 -> No working LCD devices