have a read of how-to-get-the-best-out-of-this-forum
what baudrate and protocol are the RS485 devices using? e.g. modbus
what rs485 shield are you using on the Arduino?
recommend you get a USB-RS485 dongle for a PC - very useful for debugging
which Arduino are you using? recommend one with hardware serial ports, e.g. Mega, ESP32, etc
what Arduino is the ethernet connected too? what ethernet shield?