A jointly payable Treasury check is almost certainly not a recurring payment. It can be indorsed on behalf of the estate of the deceased payee if the indorsement comports with Treasury’s requirements (signed by the executor and identifying his/her capacity (as executor of the estate)). It would also have to be indorsed by the living payee. The formerly joint account is now owned by the surviving co-owner, so he or she would be receiving all of the proceeds of the check if it’s deposited to that account. The estate would not receive any part of the check. That could create a problem if there are other beneficiaries of the estate who claim an interest in the proceeds of the check.
Depending on the circumstances, there might be no problem. On the other hand, if the check is substantial and there are other estate beneficiaries, the surviving owner of the account (who is the other payee of the check) should put an appropriate portion of the proceeds into an account of the estate.