problem with updating a shallow clone via a branch fetch

So I have a git repo that is shallow cloned:

  % git clone --depth 1 <repo url>

Sometimes (very rarely), when I do a branch fetch to update that repository I get an error:

 % git fetch origin +refs/head/<branch>:refs/remotes/origin/<branch>

fatal: did not find object for shallow <hash>

There are only 3 mentions of this error on google, none of which are enlightening. The error is being emitted by receive_need(void) in upload-pack.c. The commit in question exists in the named branch in the upstream repository, and I'm not aware that anything sketchy (forced pushes, etc.) has gone on. I'm going to continue to research the history of the repo and the deployment, but I can't seem to get any insight on what the error actually means (i.e., what conditions would cause this error to be triggered).

Any help is appreciated, Rick