That'd be my guess.  I'd maybe start with a call to your stakeholder liaison at IRS.  They should be able to connect you directly with someone at IRS who can go over your client list and see if this is widespread.  If you have been hacked, they can also walk you through the notification process.

Or check the PTIN system to see how many have been filed using your number?  I don't know how often that system is updated.

Rejects for taxpayer or spouse or a combination of both?

Ive seen multiple people over in TurboTax with a similar issue, one even called IRS and IRS said they had no other return filed for that SSN and didn't know why it would reject for that, but filing by paper was their only option.

I would call the IRS Efile Help Desk. I've had them work miracles before with efiling problems. Even if they can't fix it, they would probably be grateful to be made aware of what's happening.

Also, consider checking Where's My Refund at irs.gov. See whether that system acknowledges having received the returns.

What was your solution to this?  I am having the same problem and with multiple accounts but am not getting anywhere with the help line or IRS!