Custom Teams App not starting on MS Teams mount

[quentin-pla]

Hello I encountered an issue only when I'm opening Teams client for first time on web/desktop.

I have a custom app uploaded into Teams Applications, I added it as personal and also channel app.

To reproduce the issue, here the following steps :

Teams Browser

1. Open/Reload Teams on any browser.
2. Go to the channel that includes custom tab app.
3. Click on the tab of the custom app.
4. Open devtools, in the network panel you will see that the initial request to custom app is cancelled :
   
5. App will never start until user click on tab and manually reload app.

What is really strange is that if I click on Notes tab in the channel before clicking custom app tab, the app will works... here the steps :

1. Open Teams on any browser.
2. Go to the channel that includes custom tab app.
3. Click on "Notes" tab of the channel.
4. Wait until Notes app is loaded.
5. Click on the tab of the custom app.
6. It works.

Teams Desktop

This is exactly like browser, but it occurs only on Teams desktop startup or when switching tenant.

[sayali-MSFT]

@quentin-pla ,Thank you for bringing this issue to our attention. We will look into it and get back to you shortly.

[sayali-MSFT]

@quentin-pla ,The issue often stems from how and when microsoftTeams.app.initialize() is called. If it's triggered too early (e.g., before the DOM is fully ready or before Teams context is available), the iframe may unload or fail silently.

Teams apps need to import and initialize teams-js when running inside of Teams. More information can be found at: https://www.npmjs.com/package/@microsoft/teams-js. If an app does not perform this step, it may eventually time out and display a warning/error, as we assume the app has failed to load.

[quentin-pla]

Hello @sayali-MSFT,

I'm sorry but this is not due to this. It's internal to Teams...

I've tried to install 5 apps from the store and for all of them it wasn't working.
(Youtube, Shared Calendar, Kanban Task Board, etc...)

Here a video to explain how to reproduce on web client :

What is really strange is that, if I open "Notes" tab before any apps just after reload, all other tabs will work at first time.

Thanks.

[SeleneSSI]

@sayali-MSFT any update here?

[sayali-MSFT]

@quentin-pla ,We were unable to reproduce the issue on our end. If possible, could you please share the error logs or any additional details to help us investigate further?