When going through the YouTube API OAuth flow, brand accounts that are managed through YouTube Studio are missing.
Going through the OAuth flow you have to select your Google account, and then you're prompted to select your account or brand account. Here I notice that Brand accounts you received access to through the Brand account's permissions management are shown, but the ones you received access for through the YouTube Studio permissions management do not.
I cannot seem to find anything about this, so I was wondering if anyone knows whether this is intended behavior or not?