This is a known issue,
in order to keep logs manageable, we rotate our log files on a regular interval.
While this is done outside of production hours, it will unregister all registered endpoints.
Normally this isn't an issue as most systems will register within few seconds,
However systems that dont send out registration requests frequently, Polycom in particular, will stay unregistered for longer periods of time.
An easy way to fix this is to wait a little while, you can also trigger the systems to try a registration by restarting the system or turning the registration off then on from the admin interface.