Did you get the IRS 6475 letter yet telling you how much the IRS says they sent you ? Those are still being mailed out. Is it possible that they sent out some of the stimulus based on the 2019 return and then sent more later once the 2020 return was processed or reprocessed once they took the unemployment or PTC adjustments into consideration?
Sadly if the IRS says the entire 1400 was sent but you disagree then you will need to have a trace put on the missing money ...
https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-p...
