Approximately 15 minutes after logging in to access the Power BI apps in our tenant (the inviting tenant), our external/guest B2B users see a "Your Power BI session expired" prompt, and are then redirected away from our Power BI tenant and are unable to navigate back.
Where the user is redirected varies based on the user licensing scenario (note: all of our external/guest B2B users have a Power BI Pro license directly assigned to them in our tenant):
1. Users that have a free Power BI license in their home tenant are redirected to their home Power BI tenant site/workspace.
2. Users that DO NOT have a free Power BI license in their home tenant are instead redirected to the Power BI signup page.
Other notes: 1. This seems to be occurring across all browsers. 2. Users are able to re-gain access to our Power BI resources only after signing out and back in, however, their sessions are always limited to 15 minutes. I have confirmed this affects external/guest users of ours from multiple tenants.