Kaiser Permanente interview questions

Applied online, 24 hours later completed assessments, 48 hours after assessments email for interview. Went in for the interview(panel) and offered a contingent offer upon background and drug screen. Completed all this within the 48 hours I was required, and the next day I received a voicemail advising that the job offer had been rescinded due to my references. I have used the same references for my last 3 positions- and never a problem. I contacted all references and they stated that they never received a call from the screening group (First Advantage)? All previous references/managers and I are still in "good standing" and I have never left an employer other than resignation or lay off. CONFUSED!!!???!!!