After multiple installs of the latest SfB 2015 CU (6.0.9319.619) we have hit a bug that we're about to log to Microsoft. The bug is in relation to how you have your queues setup and as such you may not experience it.
Sales Hunt Group, when the call come it presents to agents in primary group. If the agents ignore the call then after 10 seconds the call will time out and pass to the secondary group. If no agents answer in the secondary group then it goes back to the primary (its a circular loop).
Pre CU 6.0.9319.619 this worked.
After installing the latest CU the call flow would never loop back around to the primary group (no calls present). However the caller continues to hear ringing and as such could believe that they are simply in a long queue.
To fix this stop the Response Group service
Then from Programs and Features, click Installed Updates and search for "Response" and remove the latest installed patch (sort by "Installed On"):
After uninstalling note that all versions move to the previous RG version:
Going to be logging this with Microsoft and will update as I go. Appears that I'm not the only one to have seen this:
I am dealing with the same at the moment. Nested call queues do not complete final timeout out action and continues to ring. Same CU installed. Restart of services did not fix it. Reboot of pool did not fix it either. Opening a ticket with MS today.— David Ponce de Leon (@DpdLeon) October 22, 2021
Tested and the same issue is NOT present in SfB 2019 with the latest CU (7.0.2046.369)
9th Nov 2021
Finally got around to logging with Microsoft support today: 2111090040003718
10th Nov 2021
Response from Microsoft: ""After Installing Latest Skype For Business Server 2015 Cumulative Updates (6.0.9319.619) Response Group Service Call Does Not Work For Nested Queues". This has been identified as a known issue and the Product Group is currently working on the fix on high priority"