Putting aside the 485 issue which i can't comment on, Are you saying that the directional active wires of these 4 motors are connected together?

If so that's your problem.

Tubular motors (with few exceptions) leak voltage out of the unused active wire assuming they are controlled by switching power between 2 active wires to start with.

If we say active 1 is up and active 2 is down.

When you feed power into active 1 of a motor it will go up but also leak voltage out of the active 2 (down wire). When you have motors wired together, the voltage being leaked from all the motors active 2 wires is feeding all the other active 2 wires and trying to make the blind go down at the same time as you are telling it to go up. If you disconnect all but 1 motor from that group of 4, i'll bet the remaining motor works.

Different motors can display different symptoms when this happens, sometimes you get no reaction, sometimes you get buzzing but no movement, sometimes you get some movement but it is very jittery and odd (this is common for Somfy) i have even seen blinds within the group go up one at a time with one starting as another stops. There can be all sorts of odd behavior.

One of the jobs of a Somfy "Moko" that you connect motors up to is to disconnect the unused active wire and stop the voltage from going to the other unused actives.

Hope that helps.