Currently have Polycom VVX310 connected to Plantronics CS520's via Plantronics APP-51 EHS. Having a high failure rate with the APP-51 cables. Fix has seemed to be to replace the cables. Stepped through troubleshooting with Plantronics and ultimately decided to RMA the cables. Curious if anyone has experienced this same behavior with APP-51 cables, or if there is any additional steps on the phone that may aid in troubleshooting.