my car is mini copper s s 56 2012

Problem started when car turned off in traffic sign and half engin logo papered loos of power i thoght main HP full pump gone .... Hoever i have taken the car to my home i removed rear seat to check the fuel pump ... I found the tank was empty!,,,,, there is no fuel in it.. when i remove the filter side i found the tank all most full ! I was wending why the fuel from B side doesnt go to A side where the fuel pump located ? And the fuel lines in the dashboard showing 4 lines i fill the tank with 2 galloons and the car start fine... when fuel guge droped from 5 lines to 4 car turned off.
The qustion why the B filter side doesnt fill A side ?

 

Update..
When the fuel Gage shows 1/4 tank, I run out of gas. the issue to the fuel levels not being equalized between the passenger side (fuel filter side) lobe and the driver side (fuel pump side) lobe. I have fully removed the fuel pump and fuel filter housing, checked and verified that both fuel level sending units are within specification . Excess fuel from the fuel filter housing is supposed to return to the fuel pump and suction transfer fuel from the passenger side lobe to the driver side lobe to keep both sides at the same level. I have verified this is not working as the driver side lobe is completely empty while the passenger side lobe still has a few inches of fuel.
is my lack of fuel transfer an issue of the solenoid or a valve ? do I need a whole new fuel system assembly?

 

Sounds like the pass side pump is bad. The level sensors too. Replace both pumps. Make sure the level sensor isn't tangled with the tubes in there which is common. If everything looks fine replace both pumps.