Never mind.   PPE said:

Both payments were correctly shown on the Rebate Recovery Credit worksheet and lacerte input screens. 

That said, I could understand if the client said they did not receive a payment or two and the IRS adjusted the return to reflect.  That would make sense.  However the Client did receive both payments and both were included in the input screen and Rebate Recovery Credit worksheet.

This seemed to be a recap:

MFJ, 2020 AGI $161,811, with one qualifying dependent for RRC. 

The RRC for the family: $3,517.  

EIP's received: $1,066 + 515 =  $1,581

Line 30 as filed: $1,936 ($3,517 - 1,581)

Somehow IRS reduced it further by $1,581 to 355. 

The only question I could imagine:  Did each spouse receive the identical amounts in EIP's?  (MFS in 2018 and/or 2019, splitting the income and had the same AGI??)

In any case, I give up.  I did promise to digress.   Good luck and I look forward to the answer, and hope to hear it was an IRS mistake.