welcome to the Polycom Community.
UCS 5.0.0 is a completely outdated Software and you did not post the SPIP450 Software Version in comparison.
In order to troubleshoot this we require a wireshark trace and phone logs.
Please work with your Polycom reseller to brings this to the attention of Polycom support.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Polycom Global Services
If official support is required please check how to phone or open a case here
The title Poly Employee & Community Manager is a community setting and does not
reflect my role. I am just a simple volunteer in the community like everybody else. All posts and words are my own & do not represent the views of Employer. ----------------
Notice: This community forum is not an official Poly support resource, thus responses from Poly employees, partners, and customers alike are best-effort in attempts to share learned knowledge.
Please also ensure you always check the VoIP , Video Endpoint , Microsoft Voice , PSTN or other FAQ's in the different sections