Hi, not sure if anyone encountered a similar issue.
We had a front facing MS Teams for users and added another communication sharepoint site's list as a tab in the front facing teams.
We created a powerapps form as our custom form in the sharepoint list. When we click the "New" button in the list, everything worked as planned.. The user is able to open the powerapps form via MS Teams authentication (SSO).
However, after clicking the list refresh button several times, when we tried to open an existing list item or click the New button again, the powerapps form prompted the user for login. When the user tried to login or entered his credentials, an error message is shown to the user.
The form will only open without the login prompt when he navigates to another powerapps app in teams but the same issue will happen when the list is refreshed.
See the screenshots below:
After experimenting with the front facing MS Teams sharepoint site, I found that powerapps form in the list in the MS Teams sharepoint site will work properly with SSO.