UWP App Won't Start

I have a UWP app. I'm using Visual Studio 2017 15.4.1. The UWP app is a store app and has been deployed to the Microsoft Store. My app was working fine in the store, and it was also working fine when I hit play in Visual Studio. Then recently, an isolated storage issue started occurring so I went in to the app in "Apps & Features" and hit Advanced Options -> Reset. Somehow this has fried my app installation on my machine. Our app no longer shows up as an installed app, and when I try to install the app from the store, I get an error with a code of 0x80073CF9. So, I can't uninstall, or reinstall on my machine. I've tried running sfc /scannow etc. to find out what's wrong, but nothing seems to help.

This wouldn't even worry me too much, but I can't even develop right now because when I try to run the app from Visual Studio, I get this error:

In order to debug this project, you must consume it from a Windows Store app project that creates a package and is marked as the Startup Project

I'm getting this error in the output window from the build

4>DEP0700: Registration of the app failed. [0x80073CF9] Another user has already installed an unpackaged version of this app. The current user cannot replace this with a packaged version. The conflicting package is [APP NAME] and it was published by CN=[Publisher].

What did I do wrong?

You can use Get-appxpackage -allusers *<appname>* | Remove-AppxPackage

The allusers option is important here.

You can also try to manually remove the content of the application cache folder in C:\Users\\AppData\Local\Packages\. If you have one locked file here, the whole deployment will fail.