2014 Prius hybrid engine misfire? code P301,P302, P304

Hello fellow Prius owners,

I'm reaching out for some assistance with my 2014 Prius 4.

In March 2022, my catalytic converter was stolen. I initially wanted to replace it with an original one from Toyota, but they were back-ordered, and I believe they still are. After waiting for about 8 months with my car parked, I opted for an aftermarket catalytic converter from eBay for around $140. I had it welded at a muffler shop, which caused the check engine light to come on due to the O2 sensors. However, I wasn't too concerned since I knew the cause, and the car drove without issues. At that time, the car had about 120,000 miles.

Now, with the car at 155,000 miles, I experienced a problem one morning. After starting the car, the engine made a loud knocking noise that lasted for a minute or two but then went away, and the car performed well with no power loss. When I scanned for codes, I found P0301, P0302, and P0304. I replaced the spark plugs and ignition coils, thinking it might need a tune-up due to the mileage. The car drove well for about 30 miles over two days, but the engine knocking has returned intermittently and stops once the engine warms up. The car drives fine otherwise, so I'm unsure what the issue could be or where to start.

Any help would be greatly appreciated.