I can understand why this looks odd if you are not used to how professionals interact over process questions. This strikes me as very similar to how public companies 'fail' audits - which is to say that companies never really fail audits, they just have their auditors resign.
The reason for this is that, when you hire people to validate a process, most of the failure states come from processes that you are unable to verify as good or bad. This doesn't always mean that something is wrong - it just means that the validation team (or the code of conduct team in this case) does not feel, in their opinion, that they can confidently render an opinion. This is important because, at the end of the day, all these teams can do is produce opinions.
The obvious reaction is to suggest changes to the process that would allow you confidence in validation (these are called 'controls' in the auditing world). However, if the group you are trying to validate won't make your changes, then you are left in a situation where you can't be confident about doing your job. You aren't sure that anything is wrong exactly, but you are sure that the current setup won't allow you to be sure. You're faced with sitting in a situation where people expect you to validate a process, but you feel you can't - and so the only path is to resign.
However, as you can tell, there's a chance that the problem is the process verification team. Maybe they are dumb, or jerks, or whatever. If they are jerks, then you both wouldn't be able to rely on their specific accusations and it is possible that they missed things because of rudeness or incompetence, etc. So either way the sensible thing to do is not make specific accusations aside from "we don't think we can verify this process and we would recommend you take what others say about why with a grain of salt."