Check engine light turns on for a few days and then turns off for weeks/months? Code P0420 on a 2004 Honda Civic Hybrid?

Over the last year my check engine light has come on about 3 or 4 times for a few days at a time and then turns off again for a very long period of time. I know the code means my catalytic converter is below threshold but why would it turn off? Could it be something else? Should I look into replacing it or wait it out? Any advice is appreciated!

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