Hi ahad,
In regard to the issue, we have received several related issues recently, and the root cause might be related to the service upgrade for SharePoint Online, you can find more detailed information via the link below:
http://community.office365.com/en-us/forums/153/t/74512.aspx
Please see Allan MSFT's reply in the above thread. Currently our SharePoint team is doing further investigation on this issue. Once we get any new information about this, we will update it in the above thread. Apologize for the inconvenience here. In this moment, please let your customers to access your public website with a computer instead of mobile devices. Thanks for your understanding.