Did you see the program alert yesterday? Apparently they are having some issues (some returns are getting weird Failed Schema rejections), many returns are being held until it can be remedied.
So...you're saying that if the status is 'Sent to IRS' and you have a submission ID, that the schema failure is the issue.
Thats my guess....they dont show us how the sausage is made though LOL
My "lack of an actual crystal ball" prediction will be once they correct the issue, those returns stuck as Sent to IRS will get formally rejected and have to be resubmitted.