Parents filed jointly last year (2020).  Both parents received $900 each for the advanced child tax credit.  They are due $1800 on return. 

Filing separately for 2021,  dad is claiming child.  System shows dad is due $2700 (3600-900).  Mom does not have dependent listed for claiming but the system does not show that the $900 is due back.  What are we doing wrong or does the system need an update?

Anyone else experience this yet?