One thing I don't understand is why you need to connect a widget to both MCU_To_OSC and MCU_From_OSC, these sound like the in and out of the same target and there's no reason to send midi messages to both of them in that case. What's your server's midi config exactly ?
A proper config could look like this:
MCU:mcu_to_osc,osc_to_mcu CUBASE:cubase_to_osc,osc_to_cubase
Then setting a widget's target to midi:MCU would be fine to send midi to the MCU and receive from it.
Note: the input and output ports in the config can be strings instead of numbers (see MIDI configuration - Open Stage Control). In above example, MCU would take as input the first port that contains "mcu_to_osc" in its name.
(see also this post)