Code Deploy DownloadBundle Error

I've had code deploy configured and working for a few weeks. It's setup so that it goes from our CI server on shippable to code deploy. We deploy like so (in a container):

> pip install awscli aws deploy push --application-name $CD_APP_NAME
> --s3-location http://s3$CD_BUCKET/$CD_KEY --ignore-hidden-files aws deploy create-deployment --application-name $CD_APP_NAME --s3-location
> bucket=$CD_BUCKET,key=$CD_KEY,bundleType=zip --deployment-group-name
> $CD_DEPLOYMENT_GROUP

Recently code deploy has started to fail every automatic deployment at the DownloadBundle step with the error:

> The request signature we calculated does not match the signature you
> provided. Check your key and signing method.

I don't think anything configuration-wise on our end has changed since it was working a few days ago.

I've tried reinstalling the code deploy agent and removing the deployment bundles from s3 (to have them recreated by the CI script)