The waveforms show USB-485 or MAX3485 transmitting? In any case, there's a problem with TxEnable. The sender is apparently switching between "space" (active state) and high Z. This is usually the case with "poor mans" RS-485 converters that are operating TxEnable by a monoflop rather than keeping it active during the full character frame by a dedicated TxEnable signal generated in the USB UART.
Getting the correct "mark" (idle state) level on RS-485 depends on the relation between pull-up/pull-down and terminating resistors. Using termination resistors without strong pull-up/pull-down resistors results in a differential level below receiver hysteresis and accidental received level.
Possible solutions:
- use strong (a few 100 ohms)...