Restoring a Catalytic converter? P0421

When I got this car, it had a check engine code P0421 - ‘Warm up catalyst efficiency below threshold’.

This is the front pre-cat on the radiator side.

I took it off, and soaked it for a while. Looked fine, and I could see daylight through it. Replaced both gaskets and O2 sensors. Checked for leaks, all good.

Cleared the code, and took the car for a drive today, about 40 miles.

The check engine is no longer on, but there’s a P0421 code in Pending - Which I don’t know if that means it was a known issue it’s looking for, or something is still triggering it.

Anyone have any ideas?