All you can do is WAIT ... eventually the IRS will get to your return in the MILLIONS of returns piled up for review and recalculation. Once the return has been processed the advance CTC should be released going forward but any missed payments will be reconciled on the 2021 return.
I just checked on my addendum return status on the IRS website. It said to give 16 weeks with 3 additional if it was submitted through the mail.
Even during “normal” times it takes about four months for the IRS to process an amended return. During the pandemic and due to the severe backlog at the IRS it is taking much longer—six months or more for many amended returns. Do not expect quick results from amending. When the IRS issues a refund for an amended return it will be by check. They do not make direct deposits for refunds for amended returns. You can watch for information here:
https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1