Microsoft has confirmed an issue with Polycom VVX handsets connected to Office 365 Skype for Business online.
The handsets are continuously attempting to download a firmware update that was published in Office 365 over the weekend. The update then fails to install, forcing the handset into a continuous reboot loop.
One thing to note is that currently, setting Set-CsIPPhonePolicy -EnableDeviceUpdate to $false has no effect and does not prevent the update from being pushed down to the handset.
Microsoft is working to resolve this issue.