Repository Migration to Gerrit, git push --mirror returns refs/meta/config (cannot delete project configuration)
The refs/meta/config ref is indeed only for Gerrit-specific settings (including but not limited to access control settings) for the project. Depending on the source and target it may or may not make sense to migrate it, but you can't do it via --mirror since that's equivalent to deleting and recreating the ref and Gerrit explicitly prohibits deletion of refs/meta/config.
What you could do is mirror all other refs and manually copy the state of the refs/meta/config branch, if it's something in there that's worth keeping.