error handling: git cannot lock ref: is at x, but expected y

Continuing my catalog of git errors (and how to resolve them), yesterday offered a brand new one for me.

I was trying to push some local changes up to a remote branch when I received the following error:

$ git push
Enumerating objects: 12, done.
Counting objects: 100% (12/12), done.
Delta compression using up to 8 threads
Compressing objects: 100% (6/6), done.
Writing objects: 100% (6/6), 666 bytes | 1024 bytes/s, done.
Total 6 (delta 4), reused 0 (delta 0)
remote: error: cannot lock ref 'refs/heads/pd-2750/unified-nav-bar': is at 7d4991604e851ad1c0b5ee85af7cd48b09425c16 but expected fc1af5b421553603f174a84ff4319a79945097e3
To xxx
 ! [remote rejected]       my-branch -> my-branch (failed to update ref)
error: failed to push some refs to 'xxx'

It’s worth noting that I was the only person working on this branch. (Based on reading about how others handled this, it appears that can be a source of issue at times.)

In my case the solution (though not the cause) was ultimately very simple: run git gc.

I went with the gc approch versus some more destructive approaches of wiping away the branch on the remote as a first step.

And, while many of the suggestions a StackOverflow conversation related to a similar error suggested more targeted pruning, e.g.:

git gc --prune=now
gitr remote prune origin

I just let git do its thing without any targeting or specific pruning and the issue resolved itself.