I may have to disagree with this one. I was doing some research on this when I ran into the below text on USCIS page. Shared the link below. Looks like AC21 clock is reset for interfiling.
"If an employment-based applicant requests to transfer the adjustment application to a different employment-based category based on a new Form I-140, the applicant may not utilize the portability provisions, if applicable, until 180 days or more after making the transfer request. The applicant?s new job offer must be in the same or similar occupational classification as the job for which the petition was initially filed. In essence, transferring the basis of the adjustment application resets the adjudication clock for purposes of portability eligibility.[13] "
https://www.uscis.gov/policy-manual/...rt-a-chapter-8