We discovered an issue with Stolon that was preventing failed keepers from getting cleaned up as expected. This issue has been patched and addressed with release v0.0.29.
You can upgrade to the latest release via:
fly image update --app <app-name>
Also, as a side note:
With this upgrade, you should also no longer need to export any additional environment variables in order to leverage stolonctl commands.
If you have any questions on this, just let us know!
cc:// @iangcarroll @LeoAdamek