I’m the one who originally applied is-a.dev for the Public Suffix List in this PR: chore: add `is-a.dev` by wdhdev · Pull Request #1949 · publicsuffix/list · GitHub
I believe Vercel has a very significant lag time for pulling from the PSL as we were added 5 months ago and it is still requiring verification at the root. It would be good if Vercel could setup an automated function to auto pull the PSL file at https://publicsuffix.org/list/public_suffix_list.dat every week or so in order to prevent issues like this.