<< withholding en banc court ruling? >>
It would not be unusual for a court to notify attorney's of record of an expected date and time for a ruling's release by that court.
It would be unusual for a court to release the results of that ruling to attorney's and fail to docket that simultaneously since most every court has gone digitized. An exception to this would be in some cases where a verdict is announced one day and the supporting detail memorandum is released shortly thereafter. There have been one or two examples of this in F/F cases already; I seem to recall Edwards v. PwC was one such example. But the delay in providing the full ruling was only like 24 hors or so.
However, I suspect your real question is if some controversial ruling has been released to litigants and defendants and is being withheld for some sensitivity reason. The answer on this would be absolutely not. The court will redact its filings, if necessary, but will never conceal its rulings.
JMO.