Why does AI code look ok in IDE but behave weirdly on prod

Not an AI bad take, its clearly useful+ time efficient but this is ne specific failure mode that seems to show up more with ai written code

code reads fine and passes the tests even goes thru review and then does something subtly off you cant reproduce locally. When you finally trace it this is usually odd in terms of structure, works but built in a way nobody would actually write it so nothing jumps out reading the diff. review misses it because the diff only shows what the code is supposed to do but does not show how it would behave under real traffic or other aspects you get only when its at prod

the only thing thats helps it is watching runtime behavior after deploy, something like hud or a profiler since thats where the weirdness actually shows. Things might seem ok from our end but we get to know that it failed days later or a certain feature is jumping back and forth days later from the tickets which is embarrassing

Hardcore testing before deploying is the thing now it seems, how are other devs handling this cause sometimes the bugs still leak to prod, and debugging in prod is a whole different pain. tips on avoiding that??