I e-filed my amended return for 2020 and it was accepted on May 11th of this year. I added a w2 I had forgotten and an education credit. It still has not processed and the website is telling me to call, but when I do it says they're receiving a high number of calls and hangs up on me. It is well over the 16 weeks and still no answers. I also believe it is affecting my advanced child credit, as it says it's pending, and will not allow me to make any changes and I have yet to receive any payments.
It takes 16 weeks to process an amended return in normal years. This year was not a normal year and the IRS is extremely behind in processing. All you can do is wait for them to get to your return.
First amended returns this year taking 6 months or longer to process and you are correct in assuming that the amended return has stopped or delayed the advanced child tax credit payments. There is no way to track this and there's nothing you can do to speed up the process so all you can do is wait.