You gave a couple more clues.  Forget my rambling about NRA.

Client claimed $1,936 of RRC on Line 30 of Form 1040.

IRS adjusted it to $355.  (Thus, Client was eligible to something.)

The difference was $1,581.

By shear coincidence, Client received a total EIP of $1,581  ($1,066 Payment I, $515 Payment II, per Gibraltar-solid info).

Just wondering (without know the IRS system): Was it possible that the EIP payments were entered twice into the IRS system?

A totally wild wondering, without bourbon.  

Joshua Naught, CPA