They should be doing this under warranty, correct? It's possible that it's bad again, but not common.
If you want to try it yourself, it isn't hard to do.
1) Allow the vehicle to fully cool off.
2) On a level surface, safely lift and support the vehicle.
3) Unbolt the flange bolts from the rear of the exhaust manifold and the opposite end where it bolts to the muffler.
4) Disconnect the oxygen sensor and remove the converter and pipe.
You may want to do this and check the wiring at the oxygen sensor. Do you know if they replaced the sensor when the new converter was installed?
Let me know.
Thursday, February 11th, 2021 AT 6:19 PM