Industrial environments are noisy. If your Modbus cable is running parallel to high-voltage power lines or VFD (Variable Frequency Drive) cables, the "missing bytes" are likely being "killed" by interference.
Ensure your Data+ (A) and Data- (B) lines aren't swapped.
In the Modbus Poll software, the default timeout settings might be too aggressive for your hardware, especially if you are using wireless bridges or slow cellular gateways.
