Jensing

I’ve had 2 o2 sensor codes, both downstream. I replaced both sensors, but it didn’t do anything. I’ve read there’s an issue with PCMs in these, but that normally throws the code for all 4 not just 2. I’ve read it could be a clogged cat, but I don’t notice other symptoms(rotten egg smell or sluggish performance). I’ve also read about a fuse which I haven’t checked yet. Lastly I've read it could be a bad ground. Any other ideas about why they would both be going off at the same time, but not the upstream?