Very excited to see the new tabs for Planner within Teams. Now I can view Charts and the Calendar right in Teams, very helpful and long needed. However, these tabs are not visible using the Dark theme or the High Contrast theme. Fix the bug please!!!
Not having this issue, Planner works regardless of Theme, tab works, and can add new tabs fine in those Theme's. Have you tried in the Web version at teams.microsoft.com? if your good there, you might have to look into removing cache in Teams.
The tab for Planner works but once you are viewing your Plan within Teams you cannot see the sub-tabs for the Charts and Schedule when using the Dark theme. See the jpgs I posted. Note you can hover over where they should be located and you will see them. Its a visibility issue with the other themes. Same issue occurs with the web version.