Sounds like several fundamental workflow issues that the LLM is perhaps exacerbating but need to be fixed either way.
One, they need to run their code. Make sure it works before submitting a PR. If someone submits code to me that does not work I don't care if it came from an LLM or not, go run your code and come back when it works. If they routinely refuse to run their code and never learn their lesson then I might suggest they find another profession... Or require they submit a video of the code working.
Second, going away and coming back with a totally different PR I give the feedback of "what happened to the code we were working on before? We didn't need all new code." As the senior my time is worth (a bit) more than the intern's so I don't hesitate to make their bad choices their problem. Come back when you've made a serious attempt and then we can discuss it.
One, they need to run their code. Make sure it works before submitting a PR. If someone submits code to me that does not work I don't care if it came from an LLM or not, go run your code and come back when it works. If they routinely refuse to run their code and never learn their lesson then I might suggest they find another profession... Or require they submit a video of the code working.
Second, going away and coming back with a totally different PR I give the feedback of "what happened to the code we were working on before? We didn't need all new code." As the senior my time is worth (a bit) more than the intern's so I don't hesitate to make their bad choices their problem. Come back when you've made a serious attempt and then we can discuss it.