Following up thread940-1590784 with a fix.
Our call centers use 5420 handsets and the Avaya AWH-55+ wireless headset. Our agents answer calls by pressing the headset button on the 5420. We were having a problem where 3-5% of the time the caller would be disconnected upon pressing the headset button on the handset. Using the talk button on the AWH-55+ earpiece to answer the call helped slightly. If our agents answered the call by picking up the phone, there were no disconencts (and, the agent could then switch to the headset.)
The problem occurred at all of our call centers, ruling out a specific IP500, DS8, or DS16/30. The problem appeared to be somewhat timing sensitive where letting the inbound call complete one full ring cycle seemed to reduce the occurrences a bit. (We think this is why using the talk button on the earpiece helped as it may take slightly longer to answer the call this way.)
The Avaya AWH-55+ is a private-labeled Platronics CS-50 with connector changes on the base unit and a custom electronic hook switch cable for the 5420. There was an implied hint regarding issues with the AWH-55+ electronic hook switch cable and/or possible software changes on the Avaya IPO side.
After all the work, troubleshooting, and monitoring, the fix was to replace all the AWH-55+ wireless headsets (70+ units) with Plantronics CS-50 wireless headsets along with the Plantronics APV-6B electronic hook switch cable for the 5420. The newer Plantronics CS-55 with the APV-6B cable also works. Our agents are no longer disconnecting callers when answering with the headset button on the 5420 (or the talk button on the earpiece.)
Note that the AWH-55+ is now discontinued, and, the CS-50 also appears to be going away. The Plantronics CS-55 plus the Plantronics APV-6B electronic hook switch cable would seem to be the solution going forward for use with 5420 handsets.
Final note: the CS-50 is 900 MHz. The CS-55 is 1.9GHz with potentially reduced range (we tested), but, you can have more CS-55s in a caller center without frequency collisions.
Thanks again to everyone who provided assistance and ideas in the prior post.