Placing the pads of SMD components in different layers (KiCad PCB design)
It is not correct to play around with the SMT pads like you are trying to do. The component pads, solder masking and paste masking for those SMT device pads all need to be on the same layers. Just because you can edit a pad to be on some other layer does not automatically make it be connected by some magic.

When SMT devices need to connect to other layers the way to do that is with a plated hole via. For traces that are meant to connect GND or PWR plane areas often multiple vias are used to lower the connection resistance and inductance. This can be important because often the vias are the smallest holes on the board and do not represent a lot of layer transition copper. THe holes are often smaller than the thickness of the board itself.