FWIW, I do not see how an office action, in the general sense, can be considered "material" (when the Office Action includes examiner opinion, and nothing more).
I'll give two quick anecdotes.
Years ago, I was studying a file history for an opinion letter. It was a very convoluted history. A parent application was going nowhere getting around 102(b) prior art. The CIP was originally filed as a stand-alone application, citing the references of the 102(b) rejection of the parent and then, after issuance, priority to the parent was claimed in a reissue application.
While I don't know the specific intent of the applicant, the relationship between the two application was kept secret until after issuance and, more importantly in my opinion, the real importance of the references was masked as the time the IDS was filed by not pointing out that very similar claims were rejected under 102(b) and the manner in which the referenced were applied to the claims.
FWIW, I don't think the rules would let this happen now.
In a similar situation in which I was on the other side, a corresponding foreign application cited a reference that was good enough to force me to amend the claims. I cited both the reference and the foreign OA in the USPTO. The examiner ignored it and maintained more or less the same lame rejections that didn't force me to amend the claims.
My thinking in citing the foreign OA is exactly as above: the argument for inequitable conduct based on supplying the reference without citing the very information that indicates how material the reference is and in what manner.