Why do gpt-5.1 and gpt-5.4-mini behave so differently in production chatbot use cases?

I find that both are outdated and buggy as they were originally released. I know that with codex I spend more time fixing the limited effects done by 5.4 and if just isn’t worth the pain. As for ChatGPT I don’t use it enough other than I’ll pay the Piper and stick with the better models.