They have never been available. Only A01 and A03 have.
And I have registered the game in the Stadium profile.
Until now I can only see A01 -> A05. So I do not know if there are more tracks that are not available.
How big is the file TMStadium_campaign.pak in your system? C:\ProgramData\ManiaPlanet\PacksCache\TMStadium_campaign.pak ?
To me it shows 9,12 MB (9.569.544 Bytes).
If you have less, then please close ManiaPlanet, delete this file and restart ManiaPlanet again, then it should reload the file.