Hi there,
Ok , so that would work , they are half Duplex then? On pair for send and one pair for recieve 
I would definitely check the physical connections too! , RS-485 is very sensitive because of the Differential drivers used , most noise will cancel out but intermittent connection will generate garbage if it’s one wire or pair that’s effected…
You can’t use hardware flow control, BTW there is no Signal for it, Software flow control will work. (if it’s DTR on the slave end, Then it’s looking for CTS/DSR on the host end , but unusual to have hardware flow in a RS-485 unless it’s a multidrop situation. YMMV
HTH
GL 
PJ 