P0420 code 3 months after new CAT and 02 sensors installed?

Question

I had a brand new catalytic converter and both 02 sensors installed in February 2017. June 2017, my check engine light came back on with the P0420 code again. Car runs fine, no idle, no smells, no problem. I got a wifi OBDII tester, cleared the fault, and drove a while with tests running using the Torque app. Everything tested OK at first and then suddenly Catalyst Monitor Bank 1 (MID:$21 TID:$a0) went from OK to failed. (Min: 0.35 Max: 4 / Current: 0.324). What does this mean and what could be causing it?

Answer 1

screen shot of test results