Hi buildd team, a while ago the security buildds were configured so that a source only upload with amd64.buildinfo got renamed to IIRC a +buildd suffix. Don't remember the final details, but it successfully avoided problems with source uploads for quite a while now.
It seems however that buildd_amd64-x86-grnet-01 isn't configured with that setting since the php7.3_7.3.29-1~deb10u1_amd64 upload by Ondrej exposed the issue again. Could you have a look and sorry for the vague problem description, it worked so well, that I've been getting blurry on the scope of the original problem :-) Cheers, Moritz