New-MgTeamChannel fails to provision private channel site and document library

I am using powershell with New-MgTeamChannel to create private channels. 

Although the private channel is being created just fine, the associated channel site and document library is never provisioned automatically. 

The only way seems to open the Files tab manually in the private channel  via the Teams Windows App and wait for some time until the private channel site and its document library is set up.

Trying to "visit" the document library with

Invoke-RestMethod -Headers $restHeader -Uri "https://graph.microsoft.com/teams/$($destinationTeam.id)/channels/$($privateChannel.id)/filesFolder"

fails as well.

Has somebody heard of a way to start the provisioning via Graph API?