To my own personal knowledge, the CX5100 is not officially Teams certified. Using the CX5100 with the Microsoft Teams application may, therefore, show unexpected results.
The device must have worked previously with the officially supported Skype for Business client so we can only ask you to work with our Partner Microsoft on this.
From a Poly perspective, nothing has changed on our hardware, the change came with the new Teams software, so therefore Microsoft needs to look into this.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
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. If you need immediate and/or official assistance please open a service ticket through your proper support channels. Please also ensure you always check the VoIP , Video Endpoint , Skype for Business , PSTN or RPM FAQ's