ember serve and live reload results in "cannot GET /foo"

TL;DR: ember serve -> navigate to route /foo -> change template -> live reload -> "cannot GET /foo"

I have an existing corporate app that had at one point used ember-pagefront to test on pagefront, but we have since moved on to hosting it ourselves.

Since I know we weren't using pagefront, I wanted to remove config/deploy.js (which just referenced pagefront), so I thought I should also uninstall pagefront. So, I executed npm remove ember-pagefront. This completed without incident.

However, as soon as the uninstall completed, I had some weird funnel errors on ember serve running in another console for this project, so I did the obvious: CTRL+C and then ember s again.

That's when the fun started.

The server started, no errors, I hit http://localhost:4200/, the index route redirected to my app's proper start page as usual (/contacts), and I was happy - the world looked good.

However, as soon as I made a change to one of the projects files which triggered the live reload, I received following cryptic error:

Cannot GET /contacts

What? Weird. I tried everything:

• Removed node_modules and did npm install again - no change
• Checked github for the previous package.json file, did a diff - the ONLY line that changed was the ember-pagefront line, so I reinstalled ember-pagefront - no change
• Download the previous rev of the app (from right before I did the npm remove ember-pagefront) from private github rep, appros setup (npm install && bower install && ember s) - exact same error
• Tried a different browser (Firefox) - same error
• Tried an incognito tab in Chrome - same error

• Cleared cache - same error

• Checked the running production server (running the same SHA1 of the code I checked out from before removing pagefront) - and production runs fine (but it's being served via nginx, not ember s obviously)

So what in the world should I be checking? It's like ember s all of a sudden forgot how to properly route 404s. Any ideas?