MSIX Side loaded app fails to start with 'Failed due to unknown reason.'

Copper Contributor

Our application (, suddenly stopped working today with no warning and no changes being deployed. The application shows the error “Cannot open app package Reason: Failed due to unknown reason.”

Uninstalling the application and then reinstalling it results in the application starting correctly. After this when the user attempts to start the application from the start menu again, the error occurs.

Up until this issue, there was a problem that the application would not start after clicking the icon in the start menu, until the user once again clicked the start menu (or the windows search bar) after which the application would suddenly start. I have previously posted a stackoverflow question relating to this (

This is a critical error our whole system is down. Please look into this as soon as possible.

4 Replies


We've had the same issue today, it looks as though Microsoft had released a faulty version of App Installer. We have been advising users to update App Installer via the Microsoft Store which appears to resolve the issue.

We also successfully tested on your app.

@WriteinStone  Hi, we are having the same issue. I have found a workaroud until Microsoft fixes this, when the app doesnt open you dont need to uninstall and intall again to make it work, simply double click the .appintaller file and it will give you the option to update or start the app.

We've run in to the same problem. We first noticed the problem in the insider build of Windows 11, but it seems to have made its way into Windows 10 now.

One solution that we've found is disabling the update UI (i.e. removing ShowPromt="true" in the .appinstaller file), but then we're limited to doing background updates.
Hi, it’s fixed now, you need to update the app installer from the Microsoft store and it will work again.