I see two build status connected to same pull request:

create a pull request on commit ID A -> set build status with RESP API(key=pull request ID) -> delete the pull request -> create it again with the same commit A -> set build status with RESP API(key=new pull request ID)

If the first build status is failed and the new one is succeed, the workzone auto merge does not work. So I suggest to delete all build status when user create a new pull request.

I created a support ticket, and support engineer suggest me to ask a new feature here.