Update to 355 check engine/codes

1997 355 keeps popping Check Engine light on. First time code was for cats. Cats were replaced with Hyper-flows. When engine light came on the 2nd time, code said 02 sensors. One of the sensors had become unplugged from the wire harness, was plugged back in, and dealer analysis showed all 4 were now working perfectly. Now engine light has come on again and codes are PO432 Main Catalyst Efficiency Below Threshold Bank 2 & PO422 Main Catalyst Efficiency Below Threshold Bank 1. Does anyone out there have any ideas as to what might be going on??? Thanks in advance!!