Arturia Keylab Essential 61 Mk3 not opening or controlling VSTi's in Cubase Pro 13

I wouldn’t do this, at least not immediately.

Give them a call, I somehow think that ports are a bit messy, the way you describe it, and most probably they could help you out with this.
For example:

This is not correct. MCU ports should be just for DAW usage. Controlling VSTs should be done with the other port.