I braved the crowd and sent off three 2021 tax returns that I had been holding during the annual shutdown. 

All went well except for one reject that was a new one for me.  Taxpayer passed away in 2021 and the surviving spouse was still having a hard time pulling things together, hence the late filing.  The federal return rejected because the primary SSN was locked by Social Security Admin because it belongs to a deceased person.  Yes, that's why it says Deceased on the top of the 1040.

Anybody else ever gotten this one?

EDIT:  I just caught one of the IRS taxpayer service folks - my next door neighbor - and they confirmed that they have been locking deceased taxpayers SSN's due to the ever increasing volume of fraudulent returns they are receiving, especially with the Covid relief programs AND that it is likely due to the late filing that this is the first time I've encountered it.