That's a bit of a design oversight by Bosch. If you look, there's two holes in the side-cover for the electrical wires to come through, and the cover sits nice and tight to the motor, but when you have a dropper-post, the cable has to be squeezed into one of those holes. Unfortunately, there isn't enough room for it, so it holds the cover away from the motor with a rather ugly gap that lets in all the muddy water, which then fills up inside the cover.
Also, if you look at OP's cover, it also looks like it's being held off because the furthest cable back isn't routed properly. It must be trapped between the cover and the motor. the cover should be flush to the motor.