Issue: On iOS device, users with Office 365 subscription can install iOS App, launch Office software and open from/save to the iOS App directly.
However, on some CentreStack cluster, when open from/save to the iOS App and select 'Cloud Drive', instead of showing all the folders, got error 'CloudDir_Empty_Folder_Offline_Mode'
1. Make sure iOS is using SSL connection to the CentreStack server. During login, the Access Point should be https://<your Centrestack server>
And your Centrestack server does have a valid SSL certificate installed/configured. The SSL certificate is purchased from well known CA company. It is not self-signed SSL certificate.
2. The CentreStack server should support TLS 1.2
To check whether TLS 1.2 is supported, visit SSLLab (https://www.ssllabs.com/ssltest/)
Type in your server information. SSLLab will run tests and generate the report. Make sure in the report, under Protocols, TLS 1.2 is supported. The report will also show which iOS version your server supports.
Here is one article from Microsoft, about TLS 1.2
3. Also, in the report generated from the SSLab, check that 'Apple ATS 9 / iOS 9' doesn't show any failure.