Unable to initialize a repository's release notes

I would like to use release notes generated by `gren` for our Node.js server repository. Unfortunately, I am not able to configure `gren` properly. What I would like is to generate release notes (e.g. using `gren changlog`) manually when we deploy new code to our servers. We use `develop` and `master` branches, GitHub issues, and pull requests. We have some releases in GitHub as recent as 1 month ago.

What I would like to do is generate Release Notes based on all issues closed between today and the last release (1 month ago, which uses `2018.08.31-b1` as the release and tag name ). When I try to run the `gren` command however, I will get release notes for *ALL* commits in my repository (which is >5 years, and > 5000 commits). I am not sure if this is a bug due to `gren` finding the wrong tag. Any advice is appreciated!

# Some commands I've tried:
## Not specifying tag

```
gren changelog --generate --override --data-source issues
```

The output includes a release note for `tracking-info-bug` which is code from May. We've had multiple releases and A TON of commits since then.
```
# Changelog

## tracking-info-bug (30/05/2018)
/// and then like 300 lines of releases notes following...
```

## Specifying latest tag/release
```
gren changelog --generate --override --data-source issues --tags 2018.08.31-b1
```

Outputs:
```
# Changelog

## 2018.08.31-b1 (31/08/2018)
*No changelog for this release.*
```