At least on the picture in your last post the resistors R5 and R6 are 10kΩ and not 20kΩ but that make little difference. Using this module the bus gets set to 2.5V without any driver active with a difference of A and B of only about 30mV which is below the sensitivity of an RS-485 receiver. To get a good result you should use a pull up/down resistors (what R5/R6 are doing) of 600Ω - 1kΩ, at least in my experience. If you ask the RS-485 line termination calculator it says the resistors should be about 540Ω. Because the USB adapter has such resistors (a bit too big, 2.2kΩ) it might work without is but I would install another 2.2kΩ to get better results. If you have the possibility, measure the line with a scope.
Also remove the terminating resistor you have in your schematic(SCH.png) on the Arduino side because that is already on the board. If an Arduino board is not at an end of the bus you should desolder the resistor R7 from the board because that's the termination which should exist only at the ends of the bus.