When the o2 sensors get old, they don't react/respond as quickly and if your cat is nearing end of life, you can get those codes. Theory: It might even be caused by the o2 sensor ahead of the cat, if it I not responding as quickly and letting bits of (very slightly) too rich/too lean mixture, which exceeds the limits of the ecu for post cat readings.
My cats were like this at around 120,000 miles and I used to get the occasional code like this, and after replacing some sensors due to aging codes and I think a heater code, those cat efficiency codes stopped
You might have a little bit of life left in those cats
