Consider the following scenario in Microsoft Skype for Business Server 2015:
You create a Response Group Service (RGS) group.
You create two RGS queues (nested).
You create an RGS workflow.
You configure Queue1 to use the "Forward to another queue" call action.
You configure Queue2 to use the "Forward to SIP address" call action.
In this scenario, calls are stuck in the queues indefinitely. You expect that the calls will transfer on timeout to an SIP address or to whichever other option is selected.
To fix this issue, install the February 2022 cumulative update 6.0.9319.623 for Skype for Business Server 2015, Response Group Service.