Cannot access team repositories over SSH

I have configured a SSH key in my user profile and my user is assigned to a team as admin and developer. I even tried to add my user as an Admin and Developer on a specific team repository but this doesn’t work either. The clone over HTTPS is still working and even the access over SSH is working if I access my private user repositories.

Locally I have an entry in the ssh config to use a specific SSH key to access. This configuration worked fine in the past but today it suddenly stopped working.

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The Bitbucket part of my SSH config

Host custom.bitbucket
   User git
   Hostname bitbucket.org
   IdentityFile ~/.ssh/custom

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The error when trying to clone:

$ git clone custom.bitbucket:my-team/my-team-repo.git
Cloning into 'my-team-repo'...
Forbidden
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.