In order to enable verbose log on Office 365 Endpoint, proceed with the next steps:

1. Login to Office 365 Endpoint

2. Go to folder C:\inetpub\wwwroot\Office365Application\

3. Edit file web.config by changing "RollingLogFileAppender" value from INFO to DEBUG

Verbosity can be changed on the fly; no web site restart or pool recycle is required.

Do not forget to move the changes back when the investigation is completed.