Bundle splitting per page with createPages API stopped working after updating to Gatsby 4.5.0

[davidhoneyb]

After updating Gatsby from 4.4.0 to 4.5.0, the bundle split per page functionality stopped working. We use the createPages API to create pages dynamically. We expected each page to have its own bundle, but now it appears that the entire app is bundled together when running gatsby build.

Reproduction Link: https://github.com/HoneyBook/gatsby-minimal-reproduction

Each page should have its own bundle as it did in Gatsby 4.4.0. After upgrading to 4.5.0 and even with the latest version, the entire app is bundled together, and bundle splitting per page is not working in the build output.