This repo reproduces a few different issues related to how Gatsby handles updates to pages when nodes are updated/deleted after the initial build (when in development mode).

Bug 1 - Deleting nodes

Set deleteAfterMs to for instance 10000 in gatsby-config.js to reproduce.

1. A mock source plugin creates 4 nodes
2. gatsby-node.js in the Gatsby project creates pages for the 4 nodes
3. gatsby-node.js calls createPageDependency() to bind the node and the page together
4. The mock source plugin calls deleteNode() on one of the nodes.
5. Nothing is updated. Pages are not rebuilt.

Bug 2 - Updating nodes

Set updateTitleAfterMs to for instance 10000 in gatsby-config.js to reproduce.

1. A mock source plugin creates 4 nodes
2. gatsby-node.js in the Gatsby project creates pages for the 4 nodes
3. gatsby-node.js calls createPageDependency() to bind the node and the page together
4. The mock source plugin calls createNode() on one of the nodes with an updated title.
5. Since the page URL is built using the title, it is now treated as a new page and is created, but does not work. The old page is not removed, either.

The console reports:

Error loading a result for the page query in "/updated-title-of-post-3". Query was not run and no cached result was found.
Page not found /updated-title-of-post-3

While the page is presented without any content.