This is the only code the program uses, I can post the intire code (+-1000 lines) but this is the essencial. Code is exactly the same both sides.
The problem is not hardware, i can ensure you that.
This works between Mega boards (2560) and not between Nano boards (328p)
Basically i implemented a turn by turn comunication over rs485. There are X Arduinos connected by 485, each Arduino have their own address. The Arduino with address 0x00 starts comunicate, after that is the turn of 0x01 and so one..
The arduino with address 0x00 knows how many Arduinos are in the table to know when is his turn.