I encountered this recently when someone on my team deleted our old development branch from the remote. I ran this command to check the status of HEAD:
$ git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/old_dev
This command output the name of the old development branch, which no longer exists.
I fixed the warnings using this:
$ git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/new_dev
(Where “new_dev” is a branch name. Replace it with the name of the branch you want HEAD to point to.)