The FAA wouldn't have grounded them if their checks where due we would have.
Also it could have been we asked for a STE (short term escalation) and maybe that was denied? This stuff happens all the time especially when trying to route Aircraft to certain cities for the MX. Or if a Heavy check is coming up soon you try and get the Feds to give you more time so you can work it then.
The FAA already did their AD inspection and we passed with zero findings.
The only other possibility is something like what happened to American and the FAA basically changes their mind and says you have to do something in a different manor then what they previously had approved.
But all that said I heard nothing and I was there all day.