Perhaps your version-12 branch is detached from HEAD?
Here for example my develop branch is attached to HEAD -
frappe@ubuntu:~/frappe-bench/apps/erpnext$ git branch -a
develop
* master
remotes/upstream/HEAD -> upstream/develop
remotes/upstream/develop
...
remotes/upstream/version-11
remotes/upstream/version-11-hotfix
remotes/upstream/version-12
remotes/upstream/version-12-hotfix
Learn more here
Please note here what you do to fix this - that will be a reminder that will serve the community too thanks!