Sound like a dumb question but it’s not. I’m assuming you used silicone in places when you assembled the engine. If you didn’t use O2 sensor safe silicone it will kill the sensors.
I had to learn that the hard way. If you pull them out and clean them with brake cleaner you may get them back working for a bit.
The fix is to get all the non O2 sensor safe silicone out of the engine. You know what that means.
Some how, that silicone gives off vapors that kills those things. I don’t understand why but it does.
