You have your Lync conferencing set up to require dial-in users to record their name before joining a conference call. After they record their name and hit the # key, they are stuck in limbo, waiting for up to 70 seconds to join the call. There is no hold music or any other indication that the call is trying to connect.
There are 2 options.
1.) Disable the requirement for callers to record ther name. (Set-CSDialInConferencingConfiguration -Identity Global -EnableNameRecording $false) This is a workaround, and not a fix. But hey – if you don’t need this feature, disable it and go on about your day.
2.) In our case, it was fixed by uninstalling Symantec Antivirus off the server providing our file share. Simply disabling the service didn’t do anything for us, but a full uninstall did. So if you are using an antivirus or any other server protection product, begin by uninstalling or disabling it. You can then play arond with exceptions in the software if this fixes your issue.