I think that you are correct as is the OBD2 computer.

Suppose you have a plugged injector on bank 1. The O2 sensor will read a lean condition for the enitre engine and boost fuel to the whole engine because there is only 1 pipe that the O2 is sniffing.
The problem is that this will not change the O2 reading much because you still have 1 cylinder that is pumping O2 out the tailpipe. So the computer will do it again.
Eventually the O2 will be happy but the injector pulse width will be outside of parameters.
The engine will then kill fuel to a bank at a time and sniff with the O2 sensor. Bank one will show lean where bank two will sniff good. The computer then throws a code saying that you have a lean condition on bank 1.

I do not know that this is your problem but I would be interested to find out what it was.