External and Anonymous users unable to access custom Meeting Tab

Hello,

I'm developing a meeting tab app, which is yet to be published to Teams App Store. 

When the app is added to a meeting, all regular members and Guest users are able to access the app (pre-meeting/details screen, meeting chat screen and in-meeting side panel).

The problem is with External and Anonymous participants in the meeting, who cannot use (or even see) the app at all. Although, while they're in the meeting, External users can access the tab in meeting chat screen. The tab disappears as soon as they leave the meeting. The app remains unavailable inside the meeting (side panel).

As per https://docs.microsoft.com/en-us/microsoftteams/non-standard-users, both External and Anonymous users should be able to use the app as long as they're allowed by the Teams Tenant B's admin. I have already verified the following settings -