Mobile Internet TOTP Auth

I’ve several support cases where users cannot connect to NC with their OTP 2F-Auth via mobile connections. But as soon as they are in their office or home wifi everything works. Anybody here with similar experiences?

Is this a OTP 2F-problem? Can they open the login page on the mobile browser?

Oh thank you for your anser. I forgot to update this thread. In the meantime the problem could be solved. The smartphones have had wrong time settings.