Catalytic converters are very reliable today. Any problem with it is
usually the result and not the cause. The post converter oxygen sensor
may be the one acting up. You can have the waveform inspected.

Also, before jumping out and buying a new cat make sure your oxygen
sensors are working properly and the engine is burning fuel effectively
(tune up lately?)

If you just replace the cat and not fix the source of the problem, the
converter will get damaged again.