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.*
```

Start by reproducing the reported `gren changelog --generate --override --data-source issues` commands, both with and without `--tags 2018.08.31-b1`. Trace how the changelog entry point selects tags and determines the release range. Done means the command generates notes only for issues or commits since the specified previous release, rather than the entire repository history.

索引モデルが issue の本文から書いたものです。