fatal: reference is not a tree

This is the error I'm getting

gitlab-ci-multi-runner 0.5.5-1-g69bc934 (69bc934)
Using Shell executor...
Running on localhost...

Fetching changes...
Checking out 0954061d as master...
fatal: reference is not a tree: 0954061d21c614a1f4a50417c0a877136828ccfd

ERROR: Build failed with: exit status 128

I've tried the top fixes for this error on stackoverflow, namely:

git submodule sync

and

git submodule update

but those didn't help. Possibly related to https://gitlab.com/gitlab-org/gitlab-ci/issues/19 ?