F31110 fault in V90

Hello all:

We are using in our machines 3 servomotors V90 with drives:

- 6SL3 210-5FB10-2UFx (Voltage: 200-240 V 1AC/3AC Power: 0.2 kW)

Two servomotors are without brake. The third one is used with brake, because it's a vertical axis. (1FL6032-2AF21-1LH1)

We are experimenting the F31110 in the vertical motor. Only with this machine, and we have much more machines with identical configuration and we have never experimented this fault. 

The point is that we have changed the motor, the encoder cable, the power cable and the driver. And the problem is still there. We have checked without mechanical parts, that is, rotating the axis completly free. And there was the problem. So, the only thing we didn't change was the brake cable, but it works fine. 

It's not a constant fault. It appears and disappears randomly (or at least, we don't find a relationship with another thing).

We are really confused. Maybe we change the configuration to a S210. Electromagnetic disturbances? 

Thanks and best regards.