From what I understand, the report had gone through all internal vetting before being blocked by senior leadership, for fear of the potential backlash of being seen as challenging a Jewish-dominated state in Israel.
See also this piece in Jewish Currents which expands on The Guardian’s version. It’s disappointing to see former HRW Executive Director Kenneth Roth defend the organization’s decision and argue that the report’s legal argument did not stand despite not having read the report, and that HRW’s legal department endorsed it in review.