svarc:
Riva yes, they are both connected and controlled as rs485CtrlPin... I tried your suggestion with the Serial.flush() it doesnt change the result unfortunately
Just to be sure can you put a delay(1000); after the Serial.flush and before the direction change just to see if the whole string is sent. This problem seems so much like the data is not being sent correctly and this should make sure.
I'm not up on Python programming but ser.readline() can timeout if the EOL character is not received in time. What is the defined timeout & EOL character?