Profile picture not showing in ToDo Lists

Hello there,

I have successfully added a profile picture in my microsoft account. It is showing everywhere. Even in the Todo App its shown on the top left corner.

BUT

If I have a shared list of tasks there are only the Initials of the different persons in the same color. 

This is super confusing......    

Is this a Bug? 

And Yes, I have already deleted the data in the avatar folder like described here:

https://answers.microsoft.com/de-de/windows/forum/apps_windows_10-winapps-appscat_productivity/microsoft-to-do-profilbilder-werden-nicht/6a21faf0-2f95-40dc-8b5f-f6e2816d7bc0