That's the thing with aftermarket 200 cell cats. They're borderline from the get go and progressively get worse, especially with the over rich fuel mixtures remaps chuck into the exhaust.
Pretty sure Revo 2 does include a code out of the second lambda, or maybe it's only 2+ since a full exhaust and decat is a prerequisite?. Anyway, it's a simple on/off byte in the software and if set to off, the ECU no longer concerns itself with the second lambda's readings. That's a Bosch thing, not a Revo thing.
Anyway, I hope the cat sorts your issues. What one are you going for out of interest? My APR sport cat is useless and I also want to replace it with something that works.