Is the motor bracket the same one as the original?
Is it installed the say way it was originally?
Are the motor mounting bolts exactly the same? fitting the holes in the bracket exactly the same?
You can measure where the center of the motor shaft is relative to the mounting bolt centers, for each motor.
Is the tensioner installed the same way it originally was, including it's spring, if any? (if you look at your "before" photos you can compare...if you didn't take any then you'll need to go by memory, or by looking at the wear / installation marks on the mounting points, etc).
Whatever is different between the setups would have to be the cause of the problem, if the chain is the same chain as original, and there is nothing that can move or be installed differently between any of the other parts.