I'm running with this config:

GitHubChangelogGenerator::RakeTask.new :changelog do |config|
  config.since_tag = 'v5.0.0'
  config.exclude_labels = %w[duplicate question invalid wontfix changelog_skip]
  config.issues = false
end

And expecting that what I'll get is the contents of my HISTORY.md file, and only the PRs since v5.0.0 (grouped under 'unreleased'). What I'm getting is all the PRs in the project with no tag orgnization to them at all. If I throw in since_tag = 'v4.0.0' then I do get a correct section for the unreleased tags, but then the v5.0.0 tag gets all the rest of the PRs.

I tracked it down far enough that it looks like #delete_by_tag is being passed 'nil' for both the older_tag and newer_tag which seems pretty clearly wrong, but hit a timebox and didn't track it down any further.