b) Researcher reports vulnerability that falls under X
c) Since it's out of scope, it's closed as N/A
d) Report is locked because company doesn't want to publicly disclose a vulnerability in their system via the Hackerone platform
What's the problem here? Just go with normal vulnerability disclosure. Bug bounty programs are a two way street, and respecting the scope is part of that.
Edit: I guess the important part is that the researcher was then banned for disclosing the report. Seems reasonable, honestly. I don't agree with it, but I understand it.