Turns out that I run a scala-cli command some days ago to set the default repository to some internal url... something like:

scala-cli config --power repositories.default https://<internal_url>

For some reason that seems to mess with the resolver pattern, and also messed with the repository mirrors. I went to the actual config file at ~/Library/Application Support/ScalaCli/secrets/config.json and commented out the setting, that fixed it.