Teams Desktop App not loading sharepoint List in Guest account

[_poot_]

I have access to a guest Teams group for collaboration between two companies. We have a List tab added to a channel and the correct access granted. I can access the List on SharePoint via web browser, and through the Teams web app. However, the List in the desktop app tries to load for about 20-30 seconds and then says sorry it can't load. Based on what we've tried it seems to be a bug problem in Teams desktop.

[#2]

There could be two possible solutions to fix this;

1 - removing the tab from the original account and adding the tab again - by using add the Microsoft lists to that tab and use existing Microsoft Lists

2 - make sure the guest user has the Microsoft lists app installed on his/her team's desktop app since if that is not available it will not work.

Thanks,
Pervaiz Dostiyar
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[#3]

> 2 - make sure the guest user has the Microsoft lists app installed on his/her team's desktop app since if that is not available it will not work.

@PDostiyar: How can someone install the Lists app on his desktop app? The Lists app can only be installed to a channel/team as far as I know.

Got the same problem here. Guests cannot open Microsoft Lists added as tab in channel (via the Lists app, not as website).

EDIT: Did some digging and was able to figure out a workaround. In Teams on the web guests can use Microsoft Lists in Teams without any issues. 
When they use the current stable version on Teams App (Windows) then Microsoft Lists will not work in Microsoft Teams.

Workaround: If the guests enable the developer preview (currently 1.4.00.4167) then Microsoft Lists will work in Microsoft Teams teams.

[#4]

Hey Philipp, you are 100% correct the List app only works on Teams/Channel but needs to be install from the Teams App section we both are on the same page...

secondly, when you say your guest is able to see on the web version it is because the web version is always up dated one, and when it works on the developer preview that means it is coming to a public and stable version but has to wait for it....

[#5]

Just to update on this issues @Philipp Hammer the other workaround will be ask the guest users to turn on the Developer preview, wait and then turn it off, in the regular guest view it will work for you.

Regards

[#6]

From what I've got reported back; this is only an issue when the guest user uses Microsoft 365 in their own organization, and is invited as guest to a different organization (tenant); in that case the problem occurs where that user is a guest.

I've asked guests to toggle to developer preview but then the MS List tab in Teams disappears.

[#7]

Also, the suggestions in this thread do not solve this issue:
https://docs.microsoft.com/en-us/answers/questions/288552/teams-desktop-app-not-loading-lists-tab-in...

[#8]

Digged a little bit deeper into the issue.

The URL being called:
https://mycompany.sharepoint.com/sites/MyTeamsSite/_layouts/15/listallitems.aspx?listUrl=/sites/MyTe...

Returns a 403.

When visiting: https://mycompany.sharepoint.com/sites/MyTeamsSite

You see Microsoft performing a single-sign-on in the background. After this SSO, the list is available in Microsoft Teams (using Teams WebApp)

My conclusion: bug in Microsoft Teams