Nuki Partner app: First-time users are logged out automatically, why?

As a Nuki partner, I use the Web API to create sub-accounts for new staff members. Now when the sub-account is successfully created and I open the Nuki partner app on the staff member’s new Android smartphone, and I enter the newly created login credentials, the following message is shown (in German):
“Du wurdest abgemeldet weil du dich mit deinem Konto über ein anderes Gerät angemeldet hast.” (You were logged off because you used your account to log in on another device.)
Why is this? I didn’t log in on another device with these credentials before.
Thanks for any suggestions!

Hello Anne, does it also happen when you create the subaccount via Nuki Web?

Hello Stefan,
I just tried it. Created a test account via Nuki Web and used a newly setup smartphone to log in. The message did not show.