## Bug
- [x] Fixes#38047
- ~[ ] Integration tests added: do you want them added for such an unusual edge case?~ [Comment below: skipping](https://github.com/vercel/next.js/pull/38046#issuecomment-1207444526)
- [x] Errors have helpful link attached, see `contributing.md`: ~I'll wait until this approach & error message are confirmed before thinking more deeply on how to explain the error~
Sending a draft PR as reference ahead of time. 🙂
Doesn't resolve the root issue of why `_devPagesManifest.json` might fail to load. But does improve the log for when it happens. I'd suggest applying this same fix to `_devMiddlewareManifest.json` too.
<table>
<thead>
<tr>
<th></th>
<th>Before</th>
<th>After</th>
</tr>
</thead>
<tbody>
<tr>
<th>Console</th>
<td>
<pre>
<code>
Failed to fetch devPagesManifest TypeError: Failed to fetch
at PageLoader.getPageList (page-loader.js?e87a:30:53)
at _callee$ (router.js?8684:955:45)
at ...
</code>
</pre>
<pre>
<code>
router.js?8684:1319 Uncaught (in promise) TypeError: Cannot \
read properties of undefined (reading 'includes')
at resolveDynamicRoute (router.js?8684:1319:16)
at _callee$
at ...
</code>
</pre>
</td>
<td>
<pre>
<code>
Failed to fetch devPagesManifest: TypeError: Failed to fetch
at PageLoader.getPageList (page-loader.js?e87a:30:53)
at _callee$ (router.js?8684:955:45)
at ...
</code>
</pre>
</td>
</tr>
<tr>
<th>Visual</th>
<td><img alt="Screenshot of a Next.js runtime error: TypeError: Cannot read properties of undefined (reading 'includes')" src="https://user-images.githubusercontent.com/3335181/175854728-8d5c2051-1229-4da7-8af1-fc95236befae.png" /></td>
<td><img alt="Screenshot of a Next.js runtime error: Error: Failed to fetch _devPagesManifest.json. Is something blocking that network request?" src="https://user-images.githubusercontent.com/3335181/175854774-07895846-1a1c-4bb8-bf57-fa696b8c6ba4.png" /></td>
</tr>
</tbody>
</table>