Strange Voltage Levels in a Multi-slave Full-duplex rs485 bus
First, to clear up terminology, the topology that you describe is RS-422 since RS-485 is a two wire, half duplex scheme. I have had thousands of large RS-422 networks deployed without the problems you are experiencing.

Check that you are using the correct transmit enable logic. It is opposite of the receive enable logic. Put a scope or high speed logic probe on each one to confirm its state and that it has no transients.

The devices you have chosen are not slew rate limited so cable impedance, cable capacitance, reflections, terminations, and cross talk become more critical concerns. You should run a single change elimination experiment for each of these factors. 

Slowing down your baud rate dramatically may give you more clues as to the cause of your problem.

Your method of plotting bus voltages could be part of the problem if it does not employ high impedance differential sensors.

You specifically mentioned that the conditions are the same when master side termination is used. Depending on the distribution topology and clock speed, you may find it necessary to place terminations on both ends of the cable. Make sure you have pure resistive terminations - not all film resistors are.

If none of this resolves the problem, post your schematic, cable specifications, termination value(s) and location(s), and pictures of your test setup to allow further insights. You should also comment on how you took your bus measurements since the plots are obviously very low bandwidth and therefore missing important details. And don't forget to include a proper X axis scale with any such plots.