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You should tahe the readings when the charger is connected to corresponding port.
Can also use an o-scope to compare TBT SPI signals, according with the powered ports.
U2800 and UB000 are also connected to TBT SPI chips and can affect them.
May suspect UB000, as none of its ports switch to 20V.
You should also remove and check (out of board) each dual MOSFET paired with CD3215 chips; except the working one.