O2 fluctuating does not indicate it's in Closed Loop.
Normally it will, but there are instances when it won't.
Regardless, the 'miss' probably isn't related to Open/Closed Loop.
Look up the DPFE info. It's the common one and 75% chance it's your problem.
Don't "think outside the box".
There is no box.
Do it correct, or do it twice.